1991 CLIPPER 1.8 PETROL TANK REPLACEMENT

Having much trouble with engine cutting out. I think I have resolved all the electrical issues, together with the petrol pump and carb.
I have decided to replace the petrol tank and filler pipe after discovering rust specks in the filters (car was off the road for some 10 years -whereabouts unknown).
Looking for advice as to whether the petrol tank should have a 40 litre or a 52 litre capacity.
I also note that the back axle needs to be dropped (a bit a least ) to extract and replace the tank. Has anyone got a "how to" for this job. I'm sort of hesitant to tackle it in my home garage if specialist gear is required.
Any advice gratefully received
den
 

Not sure on the tank size. My tank is coming out soon so that I can clean up as my car has not had an Mot since at least 2005. All of my rear axle and components are being refurbished. I've just removed my rear axle using nothing more than axle stands and a trolley jack. Chock the front wheels. Obviously  a good set of sockets and spanners. I used plus gas on all the bolts to be undone especially the ones holding the axle to the body. I've amassed all of my replacement parts.
Catch 22. When the axle comes off expect the worse for the body mounts as they may need welding. I left the shocks loose but in place just in case. If so you may need the axle back on to move it. It's a bonus if they dont need doing.
From the fuel sender soft rubber lines to hard fuel lines I colour code mark them to save confusion and replace one at a time.  

I think (not sure) the changeover year was 1986 so yours should have the bigger tank. I thought it was 45l and 50l the two sizes?

Over here, the 84.5 was the break over time, less than 84.5 and you have a 10 gallon tank and a full sized spare tire.

84.5 and newer you have a 13 gallon tank and a space saver spare tire. … the spare tire size is the key to the change.

Spray all Axle bolts and nuts with PB=Blaster for a few days prior.  Then use a 6pt socket and a air impact or electric impact wrench only…. If you use a breaker bar you will torsion shear the axle mounts for sure… With a impact you may shear them but it is a lot less likely.

I also pre cleaned the exposed threads and nuts as best as is possible and resoaked them. Also make sure the socket is home on the nut.