Other than dimensional differences, the Kirst backplate has ears at the bottom that form a "saddle" to prevent rotation, and the backplate is not secured to the breech face of the revolver. The R&D backplate requires drilling and tapping two #6-32 holes in the standing breech to secure the backplate to the revolver frame. R &D sells or rents a fixture to spot the holes.
In the Remington types, the Kirst uses a different cylinder and the same backplate for the Uberti and the Pietta, the R&D uses the same cylinder lenght but different thickness backplates. The Pietta has a longer cylinder.
Similar differences occur in the Colt types between the makers.
Uberti revolvers, as Pettifogger said, have different cylinder dimensions, rachet diameter and cylinder length among the differences.