gear
I have posted on this before. If the hole in the gear leg is ok and just the socket hole is elongated:
Fabricate some custom washers, made from sections of heavy wall tubing larger than the gear socket. DON'T make them perfectly round, a teardrop on one end is better. Drill and ream them to a light drive fit on the bolt you want to use. Jig the gear in place with the washers and longer bolts. Tack weld the washers in place with mig or tig. One tiny tack weld let it cool off, then another tack weld. Do not get the gear leg hot. Remove the engine mount and weld around the washers. This is so much better than filling the holes and trying to redrill.
Another option is standard oversize bolts, NOT 1/16 larger but a few thousands oversize. I think you will find it is nearly impossible to do a quality job with the engine in place. If you wind up going oversize I have had good luck using a series of reamers, reaming a minimum amount each time. In other words, assuming a 5/16 bolt, start with a .314 reamer then
.316 etc until you get the size you need. Use a strong 1/2" drill motor and some good cutting oil, don't force it, don't get it hot. MSC has a website and has all sizes reamers.