How do I convert A/C pump into Belt Driven Compressor?

I have a friend thats baggin an 80s style chevy dually. He has a big mutha caddilac engine thats going in it, its older but has the original a/c pump on it. Hes on a budget so he needs to know how you convert the a/c pump into a belt driven. Is there a special site that might have the info I need or has one of you done it before and can tell me the procedure? any help will be appreciated.