Given the ease with which S&W cylinders are removed, you should be able merely to switch them out and see if the 63 part fits. I don't have all the engineering changes memorized as some here do, but I was looking at my 63-3 after reading this thread, and it occurred to me that the location of the gas ring must be the same(yoke or cylinder), and that the extractor rod must be the same length. The timing may need tweaking depending on any possible variation in the respective ratchets. This thread might get a little more expert attention in the Smithing section.
Andy