Most of the receivers that you see out there require some sort of heat treating. The good thing is that you dont need to do the whole receiver, just the trigger pin holes, hammer pin holes and the ejector. The good thing is I've been doing it as others have suggested by doing it with a MAPP torch. It works real easy and so far has done it right every time.
It sucks for his receiver and hope he can make it right. Normally, if you do a rivet build you have to press the barrel from the trunnion, thats to do it the correct way. I have read where others have carefully removed the existing rivets though and used the barrel as a buck without any problems as long as the receiver is partially pressed into the trunnion holes like its supposed to. The rivets are long enough to where they can properly swell inside the hole as well as giving a decent head on the back side. If you can get the old rivets out, this is ideal because then you dont have to deal with pressing back in the barrel. As a matter of fact, I may go this route the next time just to make things easier.