Looked in the updated TSM Service Bulletin (Service Bulletin No. 64-30, Dec 23, 1963) and it calls out the fan as being 6-blade, 17" Diameter.
EDIT TO ADD
Curious that they went back to the 4 blade fan... They must have gotten some information off of the performance. Cheaper to make 4 versus 6?
Anyhoooooo.... The one I grabbed at the swap meet is incorrect (18", 5-blade). Going to see if I can figure out what the proper application is so I can see if anyone is in need of one.