You are correct about the exhaust manifolds, however we are talking about the control valve/flapper, here, and it being original/factory/delivered on 1968 GT500 cars.
I wasn't fortunate enough to own a '68 GT500 when new, but I suspect this part, the exhaust flapper, was a nuisance part. Springs probably got weak or broken, which caused noise. The functional benefit was negligible. It possibly was the source of exhaust leaks. They got removed and discarded with most exhaust work. Service departments probably chose the spacer alternative.
All of this boils down to--not many cars remained with their original valve/flapper. I have noticed some highly original, unrestored '68 GT500s that have this part. Those cars and the SA parts/assembly documentation cause me to strongly believe that it should be considered when concours judging.
I wasn't fortunate enough to own a '68 GT500 when new, but I suspect this part, the exhaust flapper, was a nuisance part. Springs probably got weak or broken, which caused noise. The functional benefit was negligible. It possibly was the source of exhaust leaks. They got removed and discarded with most exhaust work. Service departments probably chose the spacer alternative.
All of this boils down to--not many cars remained with their original valve/flapper. I have noticed some highly original, unrestored '68 GT500s that have this part. Those cars and the SA parts/assembly documentation cause me to strongly believe that it should be considered when concours judging.