If I had mine to do over, I'd use the repro '53 Cadillac wire wheels on wide whitewall radials. I was afraid of it being too "pimp", but hell, I get all those jokes anyway, so what's the difference. I'd like it better--except for keeping them clean!
You have to be careful with that idea. Some 50's Cadillac full wheelcovers attach funny with clips, or they just don't look right on modern wheels. There could potentially be an issue with rubbing on the fender skirts with a big old hubcap sticking out, too.
Some early 50's - back Cads had dog dish type hubcaps, but I would test them out on whatever wheels you get before I'd assume they would fit the circumfrence of the hub. Also, you'd have to use some kind of truck steel wheels from the get-go, because Caprices with this bolt pattern generally don't have the bumps for any small hubcaps.
Also, these cars are pretty fancy, so you need to find a middle ground between too much razzle-dazzle, and something that makes it look like a POS out of the junkyard. I think Fleetwoods are pretty hard to make look right, because they don't accept some of the same treatments as a Caprice will and still look right. Also, beyond the weirdo's around here, they have a stigma with normal people (I'll let you figure out what that is), so you're walking a fine line looking good, or looking way wrong.