Kind does not matter as long as you use the same oil all the time. The weight is the important issue, it shoild be 5W-30 SAE.
the g20 should be a 350 and I believe the caprice is a 305 you can swap the engines but you will also probably have to swap the intake and exhaust manifolds
There is no trunk release on a 1991 Chevy Caprice.
depends on what size motor you have in it. if v8 = 18436572
should be .035
Yes you can.
Yes. 1991-1996 springs are interchangeable.
Was built for R12, should be converted to R134a
No
yes
NO, Its a Honda motor. No.
Yes, several.
yes