I went through this a year or so ago-

Remember with rebuilding, if that compressor unit has seen any trash in the system, you'll most likely see scorn cylinder walls. Then how true those aluminum walls are determines the life left. I had a car with 70 k miles and the compressor was trashed. Kept the clutch as it shows little wear.

At the time, I could only find rebuild. I got one from the big Dallas wholesaler as it came in 1 day- been fine. They told me the rebuilder's name and I found them on the net.
Later, I got a response from someone in Australia and he said new were avaliable and gave me a local contact. It was like a short block-so you reused your end plates.
As far as upgrading, it depends on the year hardware differences. The line sizes and a bunch of things are different-not just the condesor. With a conversion, R134a runs more pressure and you NEED to have a 2-stage fan would be best. AFtermarket you'll really need to crank some numbers and see if the generic (aka smaller size) will elimate the gains. Of course, any working system is better than a non-working system.
I think the 9X+ cars had a bigger compressor also, so you'd need engine brackets too. Not sure when the brake is in production- my 86' definately is early.
For the work and effort, I would replace all hoses, o-rings, dryer, and expansion valve pull a deep vacuum and fill it with R-12. Cheaper in the long run, for texas I'd like parallel R134a setup with R-12. A/C system capacity can never be too big.


Michael

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Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E