Bob Mannel's book on page 4-59 lists two fans correct for 64 1/2 air conditioning equipped cars. They are the 6-blade fixed steel fan (Part number C3DZ-8600-A or -B) and the 5-blade steel clutch fan (Part number C3OZ-8600-B). Also see appendix F, Mustang Fans, in Mannel's book.
Mannel asserts that the 6-blade fan was for dealer installed a/c systems while all factory equipped a/c mustangs for 64 1/2 were of the 5-blade steel clutch type. I'm not sure that is true. My car has donor parts (since PO ditched parts of the original a/c system) parts from an early March 64 1/2 car that had the 6-blade steel fan (picture attached), the unique thin-base fan spacer specific to a/c equipped cars, along with correct a/c idler pulley, and dual groove generator pulley (C2OF-B on pulley).
I think either fan would be correct, early 6-blade steel fan or early 5-blade steel clutch fan.
