Couldn't you modify the OE pump and make it shorter? It has the pump low down but on 'stilts' so could probably be shortened. The GEMS had a conventional filter attached to the RH chassis rail and you could fit an external pump there but you'd need to fabricate a petrol tank with the take off at the bottom as most aren't self priming. I've run a 3.9 Classic using the pump from an XJ6 so any pump intended for a reasonable sized injected car would work.

To shorten the pump would be tricky, and have to ditch the sender. I'd rather sell it as used part (mind its got 290k km), and get a new one anyway.
There are already tanks made for kit cars and off road vehicles that come with an incorporated sender, and made ready to "fit and forget". No sense to indulge in playing around ... they even accept custom sizes. Made simple :-)

Aragorn wrote:

85L of LPG is 18.7 gallons.

200miles / 18.7 gallons is 10.6 MPG
220miles / 18.7 gallons is 11.7 MPG

So it is.😀 I have no idea why I divided by 70 instead of 85.

StrangeRover wrote:

How much range should I expect from my tank..

I'm guessing it has a max capacity of around 75ltrs

From a 75ltr fill i'm getting around 185mi

That sound about right?

H

That's 2.4 miles / Litre.
Sounds OK if you're driving carefree on country roads. It's usually a little over 3miles/litre for me when on a motorway run.

Same here, around 3.5 miles per litre. Once, I managed 4 miles per litre but that was at a steady 50mph.