'65 Formula S with "factory" 727 and 8 3/4?

Wow, good thing you mentioned that. I had to get a magnifying glass out to see it but the axle is #178 and the pinion # is 34.
17 834 or 17 8 3/4 I would imagine. The codes aren't in the option code book that I can find.

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Thank you for posting.
Quoting Govier's 1991 Parts Interchange Book: build code (not sales code) 011 is 1966 A-body 3:23 SG 10" brakes 7 1/4" rear end
178 is 1966 A-body 3:23 SG 10" brakes 7 1/4" rear end
Govier does not list an A body 8 3/4" rear until 1967 and the build code then is 614 non SG and 615 SG w/ 10" brakes. Doesn't mean there was none, just it's not in his book.
I have no idea why the same rear in 1966 A-bodies would have different build codes for the apparently same rear end. Perhaps Mr. Grovier amended a later printing if error were made.
Go figure.

Also FYI, "pinion" under build code was the speedometer pinion gear #, not the rear end pinion or ring gear diameter.