How close, is to close for rad fans to water pump pulley space

Could you post more details or a picture - cause there are literally 100s of options - so I could narrow the search. And read about flex and mounting distance.

Well,... That didn't take long. I bought it from Mancini Racing. You are right. The description now says "Rated up to 10,000 RPM". I don't remember where I got the 8000 RPM rating off the top of my head. Maybe it was 10,000 RPM all along and I was just remembering wrong, or maybe I was thinking of another model. Mine is the 18" Heavy Duty Flex Fan, Part# 17018

Here's a link:
Derale Performance Heavy-Duty Flex Fans