I have seen them before . Application 65/66 Mustang V8 A/C crank pulley from what I recall. I never paid much attention to them because they were outside my field of interest. I have always assumed that they were a Ford made part but may be some kind of aftermarket pulley.
+1 on aftermarket AC pulley...I saw them a lot in California Desert area circa late 70's-80's
Never saw them as a FORD part since FORD Dealer add-ons were different parts/pieces, usually interchangable only if full sets of pulleys/brackets.
there is no ford part number on , only ''acme'' and ''FM-6317'' on the pulley face, somebody tell me its a small block add on for non factory power steering and A/C but sold by ford dealer...
Matches up to the notion these being aftermarket.
"FM-***" designates it to be a Ford Motor application while a
"GM-***" or a
"CH-***" (possibly "CR***" I cannot remember now) would designate them as GM or Chrysler intended applications.
You are welcome, Richard a.k.a. "The Junkyard Dog"~(from many moons ago)