Alternator Pulley Size and Effect on Output.108A vs 120A, Different Rotor?

[Blown & Injected]

All the ALT's I have ordered have the wrong size pulley and they all say 108A on the front half of the case where the original one says 120A.

The parts guy says he can put the bigger pulley on for me. (Big deal I can do that too, I expect the part to be right as it comes). But won't this slow the ALT down thus causing a lower output?

Also, the 108A part makes me believe they are not using a Rotor from a true 120A ALT; maybe the faster (smaller pulley) makes up for the difference by spinning the Rotor faster.

What's the Straight Dope here?

Thanks