Nice to have a power grinder but it can be done with a hand file if you are patient. I did a similar surgery for a different car entirely by taking off the lion's share with a hacksaw and finishing with the file. The hole will enlarge fine with appropriate bit in an electric drill.

Alternately, swap front covers on the alternators. Look up "Willys one wire conversion" in your search engine for a very nice write-up on alternaor guts with pictures. This way I found out the alternator I was stubbornly trying to wire "traditionally" was in fact a one-wire unit (then wired as he says it works like a charm!).

Oh, as mentioned, torque on that front bolt will be high so run the belt as loose as you can get away with!

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Mike!