OK, I am rewriting this one. I assume the unmarked butt is what you have as a potential parts gun. That gun has had the butt markings removed at some point, and I think it could be trouble. That was commonly done when someone "borrowed" a gun from the Army and wanted to remove the military markings. If the gun was military, RAC should be on the left frame "knuckle" and under the barrel as well as on the cylinder. If it is a civilian gun, the knuckle should have the rampant colt trademark, but the Colt serial number should be on the butt.
Jim