Sales Code 644 was indeed the code for the HD Fan in ‘64.
The ‘64 Tempest Inspector’s Guide did indeed note the HD Fan as associated with the 326 as Jon Hardgrove mentioned way back when.
But that was not accurate, ie., the factory issued Guide was wrong.
All ‘64 V8 Tempests got the HD Fan automatically when AC was optioned. Since it was part of the AC option “package”, the 644 was NOT coded on these builds, no additional extra cost on the Window Sticker.
However, the 644 WAS coded whenever any V8 Tempest (including GTO) was optioned with the 3.90 axle. The HD Fan was a MANDATORY extra cost option when this axle was chosen. In a GTO, the 3.90 could ONLY be had with the metallic brake option and Safe-T-Track which were also mandatory extra cost options. I won’t get into the Radiator as it was bit complicated in ‘64 for the GTO because of running changes.
The 3.90 axle could be ordered in any ‘64 GTO, regardless of carb.
I have copies of several ‘64 GTOs that were built with the 3.90 axle, all of them show the 644 code (Pontiac Plant records, Fremont, KC, and Balt ‘64 GTOs also got the HD Fan with 3.90 axle but the coding on these records was different).
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