Off the top of my head...

Looks like OEM replicas are listed as 6.25"... about an inch wider in diameter than some of the aftermarket pulleys I found.

Not sure what diameter the Moroso is, only that it says a 30% reduction in pulley speed, IIRC. My brain hasn't shifted into calculator mode to reverse-engineer the diameter.

My cruise RPM at 65 MPH is about 3500. I don't know how much higher that is than what the OEM pulley spec was designed to work with.

The car has a 26" OEM radiator, MP aluminum housing, Edelbrock pump, and uses a 160* thermostat.

There's nothing functionally "wrong" with my OEM water pump pulley. I see there are aftermarket w-p and alternator pulleys, too, but a$$ume they aren't required as long as the v-belt style is used (as opposed to the serpentine belt conversions).