One area of difference between the originals and the repros is the area under the rammer. The Piettas have the LEAST room under the rammer & cylinder pin to accomodate a conical ball. The Ubertis have more room. I like to shoot conicals but I could not get one into the chambers of a Pietta '60 Army but I could under my ASM Hartford model 1860 Army with just a little jiggling. My recollection of many years ago when I had a Cimarron 1860 Army was that there was even more room. I believe the Cimarron was a Uberti. Ihave not problem whatsoever getting a conical into any Remington.
As for grip fit, pretty much you have to stay within the same manufacturer to get grip frames to fit the screw holes. i.e. Pietta to Pietta and Uberti to Uberti, ASM to ASM. I have swapped grips from the Navy size to the Army and vise versa but always within the same manufacturer. I hate the belled/flared Pietta navy grips and have put Pietta Army grips on a J H Dance and a '51 Navy.
With over 15 perCUSSIN' revolvers, I've been called the Imelda Marcos of cap & ball.
SASS#3302 (Life), SASS Regulator, NRA (Life), DGB#129
Wolverton Mtn. Peacekeepers (WA), former Orygun Cowboy (Ranger, Posse from Hell)