Big Block Pace Cars had Blacked out rear ends.... Track 1 and Track 2 did not....... Pat, Why in the world do you feel your Pace Car isn't a Commitment Car??
All Cars that were delivered to the Zone ( With the Embossed date ) were known as Commitment Cars....
Your car can ONLY have come out of one of two different groups we know the Big Blocks were in.
1. Display Group: We know ( By proof of Vintage Pics ) that there were at least 2 Flag bearing, Blacked Out Rear End Cars ( #123 and # 124 I believe ) and one, possibly White Rear, Big Block that was on Display at the Murat Temple Lobby where the Victory Banquet was held year in year out. For sure one of the Black Tail Big Blocks was on Display at the old Indy Museum and the other one pretty much made the rounds for Chevrolet at many different Indianapolis Metro Areas where A Pace Car was to be displayed.
2. The 2nd Group: We have the Assignment Letter that shows Car # 107 and if memory serves me right # 109 were Big Block Cars set aside for members of the press. Oddly enough, these two guys I looked up there reviews and they gave the New Camaro somewhat poor reviews. The number one complaint (outside of storage space) by these guys was that the Cars they had been given to test were 6 pops. Therefore, both reviews mentioned cars they tested were "Under Powered" ......Leave it to Chevrolet not to make the same mistake twice with these two guys....
So, knowing The Brass Hat Commitment numbered Cars had at least 2 Big Blocks available to them (maybe more) it is likely that there might be at least one more car (maybe more) just like yours that hasn't been found yet.... If a car does ever show up like yours, your car might have been one of the 2 Big Blocks mentioned on the Assignment letter.