I've played with the idea my self and being an ac engineer it helps lol but I very rarely deal with car ac stuff and I dont think it will look right with a massive condenser on my roof lol The best thing to do is what others have said find a modern car and get the bits out of that but I do think it's a bit of a waste of time as It will take a fair bit of power from a air cooled engine and you need to find a good place for the evaporator were you would get best air flow plus all the other bits , but it's your choice so have crack at it
My bus does have all the cut outs and pipe work in it but not the condensor .As baywatcher says ,did some investigation into buying parts on Samba.com to get it all working but just not worth it as it saps a lot of power from the engine for not alot of gain of cooling. . Just open the windows.