Joining late but I was a production supervisor on the chassis line at Flint Assembly; a 3/8" bolt was the factory repair for a mis-hit or missing rivet.
When I followed my '87 pickup down the line as it was being built I tried to convince the guys to use all bolts instead of rivets on the spring hangers, since I knew I would be lowering my truck by relocating the spring hangers.
They wouldn't do it...
K