alternator pulley size 1976 1800

[maluminse]

I bought one from a national dealer and a mom and pop who only does fiat.

Both have pulleys that are about 3 inches smaller than the pulley on my old alternator.

The bolt is a different size so swapping likely will not work. As well AI said that the smaller pulley could cause rpm problems with the alternator.

Suggestions? Source for the correct alternator?