Believe AC was the Primary Supplier of Fuel Pumps to Ford for the I6 engine....in '65-'66. I don't think that the "Crimped style (Carter)" I6 Fuel Pumps showed up (from what I've ever seen) until '67 on I6 engines.. If the Carter I6 Fuel Pumps were used before '67, This would be the first that I've ever heard about it...
If there's a '65-'66 Assembly line pic out there somewhere of a Carter Fuel I6 pump (Crimped style) installed in a '64 1/2 to '66 Mustang, I'd love to see it.
AC and Carter both were definitely the suppliers of V8 Fuel Pumps to Ford though in 1964 1/2 to 1966.
After '66, I think Ford went solely to Carter for V8 Fuel pumps... I don't see why the 6cyl. would be any different...
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Tony K.