5 blade vs 7 blade clutch fan

Originally, the screwy offset blades were made so they wouldn`t make as much noise.
Ditto. The nylon clutch fan in my 1985 M-B has offset blades. I don't recall how many, but at least 7 and much thinner than Mopar fans. Some use those in a Mopar because they are ~1" less thick. Slant engines are most pressed for space. Jaguar fans are similar. Both bolt up to the Mopar water pump (same bolt pattern and hole for the shaft). Some other car apparently has the same bolt pattern but a thicker w.p. shaft since I once got a Mopar fan clutch that came w/ a spacer needed to make the hole fit my Mopar. Probably not Chevy since I recall those use 3 bolts (cheap bastards), so perhaps Ford.