I found this on the Cimarron website:
"The Remington model 1858 Army was one of the favorite side arms of the boys in blue during America's period of social unrest that some refer to as the Civil War. Known for its superior strength and accuracy due to the top strap style frame. This high quality
Cimarron model 1858 Army reproduction features parts interchangeable with the original." my italics on the text. As we seem to know that Pietta & Uberti parts don't interchange, maybe the Uberti (Cimarron) parts are the answer all else being equal.