Air conditioner

Ok I have 600 dollars to spend to fix my cars air conditioner I know it only needs a new compressor and dryer but I want to make sure it works for a long time and not die on me in one year. My car is a 1982 300 turbo diesel. I was thinking of going to the junk yard to find a good compressor if I cant get a new one at the price range. My mechanic said I could get the compressor from any american car with the GM-4 series something like that. What is it AC-delco or something. And I was wondering with $600 can I modify the air condtion system so it will work better and put a different compressor or will it be to much? Thanx for any help it be appreciated I'm 20 years old and it looks like im gonna keep this car for a long time and I want everything to work. Next thing to do is to fix the cruise control. I make alot of long trips and it's nice to see diesel for 1.40 or less and gasoline at over $1.80. Cant drive my 500SLC anymore that car guzzles gas like a maniac. I drive it only very short distances..