I have the R-M conversion of the '51 Navy in .38, but not the Army.
My friendly neighborhood gunsmith did drill and tap the arbor end to screw in a screw to be filed and take up the gap in the arbor hole, then chamfer the forcing cone to 11º, I believe. Stoned and smoothed all necessary surfaces, but left the mainspring as is.
It functions beautifully and dimensions are exactly the same as Uberti's '51 c 'n' b.