Thanks for starting off the discussion. I think many late model frames are made of heat-treated steel, and the heat of welding would compromise the strength. I am not sure if early V8s had any heat reatment of their frames, so that caution may not apply.
AFAIK, rivets are very strong when properly installed--If the rivet is at a red heat, then it has stretched a bit--just due to its temperature. If it is installed and peened while still stretched, it will shrink as it cools and become VERY tight. I am not convinced that you can tighten even a grade 8 bolt to provide that same clamping force. But thats what this thread is for. I am looking for comments on the relative merits.