Stripped bolt on firewall for Voltage Reg.

I have wondered that same thing. I assume the only thing to do is weld the hole up a bit.
Something else you could do is weld a nut on the backside.

Looking forward to other's solutions

Welding it closed and re-drilling seemed the best solution to me. Easier than getting to the back of the firewall to weld a nut. I’m an idiot about welding so I have no idea if it would be still a good ground.