Came with an adapter. Both pulleys same diameter 5 3/4" pulley height is 3" with adapter. Thanks!

don't know what the adapter is for but the pulley looks like a nascar pulley. the original hemi pulley that was double groove were 2 separate pullies spot welded together. the pulley you have in your picture looks to be one pulley as the nascar double groove. if my memory serves me correct.

Does appear to be Nascar/USAC.

That makes more sense. Someone told me it was a "underdriven race hemi pulley" I wasn't sure if there was a year, model difference, street, race.
What's the story behind these? Were they an over the counter part from the dealership?

Aero426 can better answer your question(s), and correct my errors.

In the mid to early 70's & latter, you could get those through Petty Enterprise from a catalog, may've been able to get from other places, I do not know.

Very cool!! Thanks for posting the pics of that book! I wonder if you could have walked in a dealer with that part number and ordered it or if it had to be through that company. Says Chrysler Corp on it