The Pietta cylinder is longer than the current Uberti cylinder, but is the same length as older Ubertis. Ihave one, a 1987 Uberti with a longer cylinder, but my newer ones have a shorter cylinder. An R&D cylinder was fitted to the older Uberti using an Uberti cylinder and Pietta backplate.
Older Piettas had a narrower cylinder locking slot and bolt head, but a new made Pietta cylinder with the wider slots and shortened about .015 will fit a current Uberti.
You just have to try them. If you are building an Uberti kit, you may be able to lengthen the frame window and shorten the breech end of the barrel to accept a Pietta cylinder, before you assemble the kit, but then the cylinder that came with it will be too short.