What would be a way to fix a mismatch in holes in steel without ruining the
temper? Specifically a main gear leg which it bolts up to a plate . Two of
the four holes are about 1/3 diameter off. The bolts are 3/8" od.

Possibilties, as I see it, a elongate existing holes in one part to fit
the 3/8" bolts; drill new 3/8" holes in new location; install 1/4" bolts in
mismatched holes. I don't have access to tooling
or machinery that could drill out the holes to say 9/16", thereby replacing
the 3/8 with bigger bolts.

Any advice would be appreciated.
Thanks, Dick