The bicycle wheel? Part of the "road test" equipment included in the kit. It's called a 5th wheel. Connected to an electronic recorder, it measured acceleration, speed and distance.
Snooze and lose.
I got one a while back. Pulled a donor kit out of my stash and it has the infamous crushed windshield posts. Looking for a proper Cadillac grille for my build. The Pontiac bar just doesn't cut it.
I managed to get one of Gerry's Mustang Notchback bodies, along with a 69 Cougar fastback he mastered and cast with the parts left over from the Mustang conversion