Found my dads original 1971 duster!

ocdart said
The clutch mentioned by Bennoel 10 in post #240 is on the other side of the fan in the above pic. Turn the fan over and you'll see the viscous clutch.

Awesome. Thanks! I’m not sure the builder wants to use it. I’m also not sure how to tell if the clutch would be any good. Looks like I’ll be buying new. I guess at this point, what another $300 for a new fan. Lol