For R134a a PF condensor is a must-have, and there are plenty of generic choices available on eBay. Just pick the largest which will fit. You need new hoses, but you needed them anyway. Any decent a/c shop can make them for you. Stick with R12, if you can, as it is available, or consider R152, which is very inexpensive, readily available, and it chills like nobody's business. Google it. I don't have a Monty, but my Euro BMW 635 has the worst factory a/c ever, and the PF, R152, and a Sanden compressor have resulted in a fairly good system. Will do the same on my '92 Spider when I get around to it.
Dean - '87 & '92 Spider Veloce's