I have never swapped the rears. I did at a show one time see a 53 ,I think it was, that some guy had fabricated mounts and had rear leafs installed. No idea what they were off of. I wanted to talk to him but he wasn't around, just his wife that only knew it was blue. But it was really neat, a lot of fabrication. The leafs almost looked like small trailer leafs. He had mirror under it, but still they are a pain to see with those long fender skirts and short sitting 50s chevys.
I remember a discussion where some used a coil over rear end for a 47ish pick up for a 50's coupe with out major modification. Not sure of the exacts, but I remember a discussion I coudn't find it on here. But I remember he went out and got measurements, and listed a bunch of specs. I will check the other "places" I am a member at it may be on there. Someone else may remember that.
Good luck, sounds like a fun project!