My headlight units don't match. I have got one silver and one black headlight. It has been like that for a bit and I thought it about time I changed out the silver one. I have bought a good black headlight but with a broken housing. The headlight itself is OK.

I thought, no problem, I will take out the original headlight assembly from the car complete with the housing then fit the replacement headlight off the car. However, I have run into a few snags. I can't get the old headlight assembly off the car. One of the bolts in front of the battery is rusted solid as well as hard to get at. It won't take a socket and really needs drilling out (not keen). Plan B is to separate the new headlight from the broken housing and fit just the headlight to the housing still on the car.
The headlight has 3 brass adjusting screws which form ball and socket joints at the rear of the headlight. The brass ball sits in a nylon cup in the plastic.
What is the proper way to separate these? it looks as though they just lever out but I don't want to damage it. Rave does not cover it.

Yes, they do just lever out but be careful, they may be a bit brittle. You need to make up something that will allow you to lever equally on both sides and not just on one side.

I can take the battery on and off mine with no issues as a previous owner must have had stuff turned off in the becm. Anywhoo, it's only a couple of bolts holding the battery box in from memory and you'll have lots more room with that out.

Lubricating the balls with some light penetrating oil makes levering them out much much easier.

Thanks guys. I have lubricated my balls, I finally got the unit apart with the help of a few squirts of WD40 lithium grease. I used an open ended spanner as a lever around each ball socket. I think I will take out the battery box next as suggested. Then I think stainless nuts and bolts all round when I reassemble it. What started out as a two hour job has developed into a two day job.

Just off-topic, reading the posts as they go along it becomes hilarious.
Make sure you always get the balls lubricated! :-)

It is known as a "double entendre", Leolito. A bit of levity after a difficult day trying to get my headlight apart. Everything I touched broke.
Good job I didin't touch my balls. Ha Ha.

Let us never lose the funny side of it all ... even ironically, as you say.
As time passes, more and more seems to be needed! :-)