I've never liked screw build AKs, although they do work. My concern is that the screws would come loose. I've seen it happen.
I've also seen rivets come loose, but I think they weren't installed correctly.
Welding the trunnion to the receiver is a good. cheap home build method, but has the down side of not being able to reverse. It is plenty strong though and has worked for H&K and CETME for decades.
Riveting is the best way I think, but to really be right, the trunnion needs to be riveted to the receiver without the barrel installed in it,