Unless you are looking for specific MG42 markings, I would just splice an MG3 rear section on from RTG, thats what I do with all my builds. I use a set Global machining shells for the rear eceiver, then cut and splice the MG3 rear on. Eliminates fitting buffer tabs and riveting them. They have the lower tab cut for the MG3 reuperator, but an 8mm type can work with them just the same.
You may get one that is tight from the demilling, but if so it can easily be expanded back out by using a rail riveting support that RTG and BRP sells. Not all of them need it, but I did get one out of 3 that did. Expanded it like this:
Some are long enough they have the rear rivet holes.