my buddy stopped by and needed a pulley for his 69 cuda. He said this one was 1/2inch, rather than 3/8. I thought it might be for a hemi, but most I've seen were solid. Any clues?

That pulley is called a key slotted pump per factory parts book and is a Saginaw. I believe most of the Hemi cars were Federal which is called the 3/8 treaded hole in the parts book. Maybe that helps.