First congrats on your journey to rebuilding the iconic Mg42/M53.
Second w/o pictures to see how badly yours are damaged it is hard to tell what you are up against;
Though the vast majority of de-milled M53kits now just give you the buffer tabs attached to a small piece of receiver, then you merely drill the rivets out-(as I am sure you know) and assess the damage, sounds like you may have a kit like the ones Mg43.com use to sell, or some of the older Mg42 4-cut receivers, where sometimes the last cut went right through the buffer tab, then the answer is, IT DEPENDS.
Usually when doing a build most people are trying to save some money, I get that, but you do not want to try to salvage a piece that will cause endless headaches when you are in the final stretch. That said, a true craftsman can fix anything, maybe you are in that category, if like most of us and you are a weekend warrior, then the question is, can you can make that piece come back to spec. In theory if you have a good jig, and you re-weld it true, and there is not weld oozing out of the channel for the buffer tabs on the buffer to rotate, it should work. I would posit so long as the corners on the tab are still true, and again the receiver is welded to spec, I have seen plenty of tabs cut in half salvaged, even the recoil plate can be salvaged many times on those old 4-cuts.
“… corporations have been enthroned, and an era of corruption in high places will follow, … until all wealth is aggregated in a few hands and the Republic is destroyed.”
- Abraham Lincoln (Republican), Nov. 21, 1864