The accuracy problem most likely lies with the bore being rifled for a round ball. The lighter (shorter) the bullet you load in a cartridge, the closer it will be to a round ball.
All the Ubertis are the same, the fluted cylinder is the same in dimensions as the full round, they just look very different because of the full fluting. I have a 2nd Gen Colt (made of Uberti parts) and an Uberti both with full fluted cylinders, they both fuction perfectly with standard round cylinders.
One of my 6 1860's works with the R&D conversion cylinder without overtravel on the cylinder when cocked fast. Certainly, the overtravel issue could be cured in the other revolvers with some spring or timing adjustments, but I left the conversion cylinder in the revolver it worked best in for the sake of being too lazy at the time to take the others apart and tune them for the R&D.
So, an R&D cylinder will fit your revolver, no problem, timing may need to be adjusted.