I'm late to the show, but kind of an A/C guru.
To convert, all you *need* is the conversion fittings. Flush system, replace accumulator/dryer, change o-rings, draw vacuum, put in 8 oz of PAG oil and the right amount of R134a.
For maximum efficiency, though, the part you all are thinking of is actually the condenser. You need more surface area for better cooling. The problem there is that R134a didn't become standard until 1993, and that is a different body style. You would have to check where the piping enters and exits the 1993+ condenser to see if it can be easily retrofitted. Another possibility I have tinkered with is to mount two exact condensers, one in front of the other, and make a custom pipe from the outlet of the rear one to the inlet of the front one. Put them as far off-center from each other as possible, while still being able to connect the front one's outlet. This would effectively pre-cool the refrigerant a bit in the rear condenser and then fully cool it in the front one. It would also change the optimal refrigerant level, though, so one would have to charge the system to spec, then slowly add more refrigerant until the air doesn't blow any cooler.
Perhaps I'll do that someday and report the results and difficulty levels for the fab work. It seems that as long as you find a way to make a pipe or hose between the two, the mounting adaptation should be pretty easy.
Last edited by DRTDEVL; 11/18/18 11:08 PM.