Gold Lifetime Member
Join Date: Oct 2001
Location: Londonderry, NH
That's the difference between the GM 10SI and 12SI alternator case.
When you buy a rebuilt alternator, there is no guarantee that it will put out the original rated current. Rebuilders have a bad habit of swapping stators and rotors and basically mis-matching components out of ignorance. If you talk to the right parts guy, you should be able to buy the proper 10SI alternator tested at 65A output for your car.
If it's still a problem child, you can upgrade to the larger alternator. I did my brothers Monte Carlo years back 'cuz it kept burning out the 65A alts for no good reason. (Actually, he runs all the accessories with the car idling a lot!) You may have a little bit of trouble fitting the larger 12SI case in your car, but it can be done reasonably easily if you really need to do it.