'67's started out with a bright trim ring (there were two early versions) that were added to the modified stock Ford rear valance that didn't have any exhaust cut-outs the cut-out were hand cut by Shelby workers' and then the trim added to dress the rough cut-out. Later the cars got the Ford GT rear valance - cheaper easier and no trim. I think the change-over was early in the '67 calendar. (I have been e-mailed that it is thought the change occurred at the very end of January)
The early cars that got the added bright trim got either a '66 GT trim that was modified by Shelby workers by cutting off a portion of the bottom (top image) or a flat piece that was also used in '68 on some special Cougars (bottom image).
JD,
I'm not convinced the that the early flat pieces used on the October '66 builds were the same as the '68 Cougar trim used.
Those Cougar drawings (Philip/propayne provided a few years back) don't look identical to what has been found on the Shelby's.
When?
As JD and Dave M. noted, the rear valance was a Ford SJ supplied part and thus the Shelby VIN number is not really relevant.
(There were SAI completed cars with four digit VINs that have them.)
The SJ build date is the important detail to follow. The change notice Shelby issued to Ford was dated in late January...1/25/67.
I also believe the change over to the stamped GT rear valance was implemented sometime in the first week of February at Ford SJ.
There some interesting conversation on this topic in the attached thread;
http://www.saacforum.com/index.php?topic=1953.0