Thanks Mike, I appreciate it. Those are great photos of the prototype Trans Am. Good catch on the "Welcome race fans" sign. That obviously shows that that particular picture wasn't taken at the GM Milford Proving grounds. I'll have to look at it closer and do more research in order to try to figure out where it could be. It could be Michigan International Speedway like you suggest because it had just opened and it is geographically close enough to Detroit to be used as a test site.
I wonder if the item you are referring to is some type of early hidden windshield wiper system being tested on the car for aerodynamics or something. I noticed that the item appears in the sketches done by designers Gene Winfield and Harry Bradley referred to in the following paragraph:
"In the Fall of 1967, designer Gene Winfield and designer/artist Harry Bradley approached Pontiac with a proposal they called the
"Firebird Can Am". Gene Winfield was actually a consultant under contract for the plastic model company AMT, and therefore had
advance notice as to what the 1969 Firebirds would look like long before they were introduced to the public. Since the Pontiac
Special Projects Group were still involved in refining the suspension for the 1968/1969 Firebird, and had gained tremendous
experience on the race track racing their SCCA 1968 Firebird, the Winfield/Bradley drawings were the first designs to seriously be
considered by Pontiac as a possible look for their new "ultimate Firebird"." (
http://musclecarfilms.com/1969_Firebird_Engineering_Cars_2.html)
Interesting that the car has Royal license plate surrounds. The hood scoops and side scoops look to be a little different as well. To me they look more angular, not as rounded.