Upgrade to stock Alternator these days for the /6?

I would FOR CERTAIN inspect the bulkhead connector and ammeter wiring. I would NOT put anything on the stock wiring larger than a 50, using stock wiring. There are tons of threads on here about this subject.

What year/ model are we working with?

Also cast a slanted eye at the "new" one. IT IS TOO OFTEN that isolated field (incorrectly called dual field) alternators come with one field terminal GROUNDED, yet the rebuilder/ manufacturer has left the flag terminal on the alternator. IF YOU use a 70/ later regulator, this means there is a 50-50 chance of problems, including a short that will burn up wiring.