Why not just put a set of Treso-Ampco, good quality niples in it and be done with it. Ampco nipples Last a lot longer, give better ignition, have less blow back problems, and are longer than Uberti nipples.
They are available from "The possibles Shop", and "Track of the Wolf". I believe the thread size on Uberti nipples is M6x.75, for a Remington.
Rebel Dave