I've heard of it being done, haven't seen it. The only dimensions that really come into play are the steering column, clutch, and accelerator linkages, I think, and the length of brake line tubing connecting to the master cylinder. Possibly the tailpipe ends and bumper brackets. I suspect none of those are real serious issues. You also will need to use cushions or washers on the mounts where the later cars don't have cushions, and on the roadster-only mounts. I would advise you to check around for the thinnest cushions (sorry, I don't know which years have the thinnest).
I will need to make that same decision eventually for my 63 roadster, but to be honest, I never considered my car to ride harshly or unduly transmit vibrations to the passenger compartment, so I will probably go with stock mounts. I briefly owned a 63 coupe, which DID have some annoying sound and vibration issues, although I wasn't all THAT annoyed... the most annoying problem in the coupe occurred while driving at speed with a window down, probably NOT related to body mounts.
That said, Chevy got serious about reducing vibration in the '62-'63 timeframe (I worked as a student intern in their engineering test lab back then, but not in that department), so they did a LOT of sophisticated testing and added cushions to most of their cars starting in 1964 (not just Corvettes)... They wouldn't have spent the money if they didn't think the result was worthwhile.
