Generators are no big deal to fix, if it hasn't been overheated to where the solder is slung off the commutator, then it probably needs brushes and the commutator cleaned, and maybe bearings, all of these are easy. The only other problem could be the regulator, and again it is no big deal. If you do replace it with a alternator, you might want to consider saving the old parts and brackets, in case you ever decide to sell it, being a 64.5 generator car, the new owners might want to put it back to original condition. Also depending on the alternator you want to use 1g,2g, 3g (Mustang Monthly has a good article on these), there is wiring involved, and your instrument panel has a gen bezel and you will have to change the panel to one with a alt bezel if you want it to reflect the change. My 2 cts. Good Luck.