I've substituted the cylinder from a Model 442 that had been modified for moon clips by TK Custom into a Model 642 without any problems at all. I recently substituted a nickeled cylinder from a Model 38 (unknown dash number) into my (blued) Model 38 (no dash) to achieve that stainless steel cylinder look found on the MSP (Michigan State Police) Bodyguard. I also substituted the narrow, serrated trigger for the wider, smooth surfaced trigger from the donor gun, and finally replaced the hammer on my Model 60-7 with the hammer from the donor Model 38. All parts in these modifications were simple drop-ins and have worked flawlessly. The Model 38 parts were purchased from a fellow forum member whose pistol developed a crack in the frame. He sold me all of the parts except the frame for a good price, and I had a good time with the project.
Best of luck,
Dave