Or you could always buy the original....
https://www.facebook.com/marketplace/item/4136918786339619/?

Agree on the lifters, there's no way you'd fit a new camshaft without new followers but it wouldn't, or at least shouldn't, need rocker pedestal spacers unless the unloaded part of the cam was at a different height to original. It would also need to be quite a way out as there is a fair amount of tolerance on the hydraulic lifters (see http://www.v8developments.co.uk/technical/valve_train/index.shtml). As long as the cam has been specifically designed for the engine then the unloaded section should be the same depth and the timing should be right so no need for a vernier.

But even old Jap bikes are going for silly money these days https://www.carandclassic.co.uk/auctions/1972-kawasaki-h2-750-MgDzJ4?. Values of things like the original Honda 400 Four are completely mental.

Seems others don't agree

https://www.carandclassic.co.uk/auctions/1971-range-rover-suffix-a-K8WdVg?

https://www.carandclassic.co.uk/auctions/1998-series-1-land-rover-discovery-v8i-xs-Jgz3dn?

https://www.carandclassic.co.uk/auctions/2006-range-rover-35th-anniversary-edition-A4wx18?

To become a classic something doesn't even have to be that desirable. People are paying silly money for what were regarded as mundane in their day. Have you seen the price a Mk 2 Escort is going for these days? Even a humble 1300 will fetch silly money, a rusted shell with a tree growing through it sold for over 4 grand recently as it still had the VIN plate and a V5. Don't even start me on VW Beetles, they were horrible when they were new but look what they go for these days......

Don't look to be a lot wrong there, combustion chambers, pistons and bores look fine. Check the head face for warp, clean it up and you'll be ready to start putting it back together. Radiator simply lifts out once the hoses are off. They did originally have a small bolt on each side at the bottom but if it's aver been out they will almost certainly have been left out. Yes, there isn't much you can't drill with Cobalt drills and a can of cutting oil, I had to drill the heads off 4 stainless steel bolts yesterday which would have taken the edge off standard HSS drills in no time.

But as the values of Classics have gone through the roof, even if they get half way, it'll be good. I paid £900 for my Classic LSE, kept it for 4 years and sold it for £2,300. I had been hoping to get what I paid for it back and was godsmacked when it went for what it did. I suspect by now, it would sell for double that despite being a bit scruffy but reasonably solid (or as solid as any Classic can be).

Your local Land Rover dealer......
https://parts.jaguarlandroverclassic.com/fvf10002l-clip.html

Just been looking at the specs for the standard cams, 4.0 litre (GEMS and Thor) has a duration on both inlet and exhaust, of 285 degrees, GEMS 4.6 has a duration of 264 degrees and Thor 4.6 is 272 degrees but the inlet opens 14 degrees earlier and the exhaust 8 degrees earlier. So the Kent cam with a duration of 262 degrees would suggest initially that it wouldn't be as good but we don't know what the timing is (and I doubt they will publish it or you could get a blank ground to match). The only thing that is different is the Kent cam has a lift of 11.2mm compared with a lift of 9.94mm. The rocker gear has a ratio of 1.6:1, so the valves will open 2mm more. However, I've no idea how, why or what sort of difference that makes, cam timing has always been a bit of a black art to me.

The crank sprocket will only go on with the mark in the 12 o'clock position when the crank is a TDC on number 1. So, following the process in the Overhaul Manual, you fit he sprockets with no chain, line up the marks, pull the sprockets off, fit the chain and then slide them on.

Assume you are setting off before the ABS, Brake and TC lights have gone out? Until they go out you've insufficient pressure in the power system for them to give full braking power, both of mine are exactly the same. They'll stop but not very well. Whether it is supposed to be like this or if the pressure is slowly dropping while parked I've no idea but if the Linley isn't then maybe it is down to slight wear in the seals inside the modulator?

Loose connector on the temperature sensor. I had similar with a transfer box overheat message and that was a loose spade connector. Gave it a squeeze with a pair of pliers and never see it since.

Sensor is the one with a pair of blue wires attached to the side of the transmission cooler down next to the LH headlight (or it is on a V8 anyway).

On a car with no TC, you can change to 2 wheel TC by changing the modulator and ECU for the 2 wheel type. Whether you can change from none or 2 wheel to 4 wheel TC, I'm not sure but it wouldn't be an easy swap. The non TC and 2 wheel TC use the Wabco Type C ECU, whereas the 4 wheel uses the Wabco Type D and they are physically different and have different connections (Type C has one big connector but Type D has three smaller ones).

It might just be that the oil changes haven't been done as regularly as they should or it's had cheapo oil in it. What's in the sump looks a bit dirty. Turners and V8 Developments are the only two places I would trust on anything to do with the engine, so what they say about the cam is likely to be correct. Price is a bit steep though. Cam timing for the 4.0 litre and 4.6 are different, (and GEMS and Thor are different again on the 4.6) and I've wondered which one out of the 3 standard ones would give the best results. That's a question for Ray at V8Dev next time I'm passing I think.

As for learning in a P38, my step daughter started learning to drive in a Micra she bought but then lost her job and couldn't afford to run it any longer so sold it. She started a degree course and got a part time job as a hotel receptionist but the buses around here are pretty infrequent and there was none at all if she worked a late shift. She asked about learning in the Ascot (my spare P38) and pointed out that it wouldn't matter if she did an auto only test as all three of my cars and her mothers Merc are all autos. Even with a provisional licence, but 25 years old, she could get Classic Car insurance on a 4.6 P38 for less than she'd been paying on a Micra. Then she went to visit her boyfriend in Holland for a couple of weeks in September while she was furloughed, the Covid restrictions on travel kicked in and she finally managed to get home a couple of days ago (after the bank of step dad stepped in to pay for the multitude of Covid tests).

I'm wondering if the engine has ever been changed or if it is just the oil that has never been changed? I would expect it to look less black than that but I've seen many that are far worse where everything is coated in what looks like, and has the consistency of, black wax. I've seen the marker writing on most engines, so it may be factory, who knows.

You'll know what the rest of the engine is like when you get the heads off and can see the bores.

I edited your post so the picture appeared.

and I bet your sidestep supports aren't rusting away like they mostly do over here....

+1 on Delphi. That's what I've always used.

No. It shouldn't drop at all if everything is perfect, so when you get in it in the morning you should still have the normal height light showing to tell it is still were you left it. If it has dropped, then it should come up immediately, within 10 seconds or so. 3 minutes suggests you are losing pressure in the reservoir and it is having to refill that before the pressure is sufficient to lift the car.

Personally I wouldn't go to the added grief of taking the front cover off, you've already got enough work on your hands as it is. Mine had never leaked even when it was up to 285,000 when the engine came out to be rebuilt. Obviously it was taken off when the engine was rebuilt but that was 135,000 miles and one replacement water pump ago and it isn't leaking now. So yours should be fine. The gasket will have been put on dry originally and the fact it is weeping would seem to suggest there's no gasket goo in there to seal it (or tear the gasket when taken off) so tightening it up when the pump goes back will close up the gap and it will seal again.

Most replacement cams are to give more top end when the engine is used in a Morgan or the like. If anything the P38 could do with a bit more bottom end grunt (or at least the 4.0 litre GEMS could) so you are likely to be in uncharted territory when selecting a cam. As you say, it isn't going to be cheap and if your existing cam and followers aren't worn the cost benefit ratio may not be sufficient to justify it.

They'll get there as more decent ones appear on the market and more people start to appreciate them. Prior to the P38 there was the Classic which was pretty basic initially and not that much different to a Defender but with added luxury features such as deeper carpets, electric windows, air con, leather seats and the sort of things that luxury car buyers wanted. But it was still the same old design underneath. The Disco 1 was merely a budget, re-bodied Classic so was accepted as a 'proper' Land Rover by the One Life bunch. The P38 was designed as a luxury car but retaining, and improving on, the off road capabilities. Being seen as a luxury car, the purists immediately didn't like it, it wasn't a proper Land Rover. The complexity, for it's time (which compared with a car 10 years newer is pretty basic), wasn't understood, even by the dealers, and initial weaknesses meant it got the reputation for being unreliable. Which, in truth it was and, as even the dealers didn't really understand it, that reputation stuck. For 97MY there were numerous minor changes made to address the weak points and the advent of mandatory OBD2 compliance from 2000 would have meant a complete redesign of the GEMS engine management so a switch to the Bosch Motronic, already in use by numerous other manufacturers (including BMW who owned LR at the time), was the obvious next step. But it's interesting to note that the One Life crowd haven't accepted anything later than the Disco but the P38 appeals to a different class of buyer.

I think I've proved that a P38 can be reliable. When they do need work doing, they are easy to work on, parts are readily available (and cheap) and I wouldn't swap mine for an L322 at all. I might swap the Ascot for one as that is a standby, ready to be used if I'm halfway through a job on mine and need to go out and pick something up, but if I've got a 3,000 mile trip to do, I know which one I'll take.