Like most parts in revolvers, the cylinder and ejector assembly is hand fitted at the factory, then adjusted for proper alignment, end shake, timing, and barrel/cylinder gap.
Once it's been fitted to a specific frame, it almost never properly fits another frame, certainly not without being re-fitted, and this usually means a factory-new ejector.
It's very unlikely to be able to just "drop in" a different cylinder AND have it be in proper adjustment and fit.
You'll often hear of people doing this , and they always report that it fit and worked.
They never tell you that the job was inspected by a trained pistolsmith and he said it was in proper adjustment.
There's a BIG difference in "getting it to work" and getting it RIGHT.
In addition to the normal problems with installing a different cylinder assembly, the lock work between a 6 shot and 7 shot S&W are different and this too requires some hand fitting of parts.
Unlike semi-auto pistols in which many parts can be dropped in with little fitting, the revolver is a throw-back to another time, in which craftsmen individually fitted parts to revolvers.
NO PART is more fitted and adjusted than the cylinder assembly.