Mine is an '86 but they should be the same. The high side valve is right on my receiver dryer. The evap core is somewhere way
inside behind the console. I'm afraid to tackle that. Most of the oil should be in the compressor and receiver dryer which
you're going to change anyway. You could flush the compressor with brake cleaner I suppose. I stuck to R12 because I have a
good supply and it is easier on the engine (lower pressure) and doesn't need the new hoses (R12 has bigger molecules so it
leaks less). Also it doesn't require an oversize condensor and does NOT have a critical temp like R134 does, so it works
better in hot climates.
-- Bob Bartch