Thanks, Jerry!
I really think it was a rogue bolt. I checked the granny bottom and to your point, only saw hex head bolts. I also looked up PG internal pics online, and saw none showing Allen head bolts.
I put a new blue Moroso gasket on the pan and closed it up. It will be a while before this truck sees the road, and will be tested in the neighborhood first. That said, if that bolt was holding something together, I guess I'll have time to find out!
