What's the best replacement AC Compressor?

[Lugnutt]

Ugh, I thought I had a good plan in place to replace my leaking junk Harrison rebuild AC compressor with one of those new aluminum Sanden compressors using R12, but after calling Vintage Air to get the correct part number, they told me I would need to replace every piece of my AC system first. They say that their 508 pump doesn't put out enough pressure to work with a factory GM AC system. Have any of you guys dealt with this successfully and what would you recommend for me to do.

Thanks all,

72 Chevy K10 350 with Factory AC