You just found about a $1500 exhaust manifold! Jackpot!
As Tim said, they were used on the '53-'54 Corvettes, but many more were sold as accessories by the dealers because they were a bolt-on for any 235 or 261. Dealer retail price back in the day? $15!!! I have read that the majority of the production was sold as dealer accessories. If we had to rely on ones that came with Corvettes, they would be even more rare. Notice how the manifold allows for the use of the heat exchanger with a stock intake manifold.
You would have hit the Power Ball if it was attached to three carb Corvette intake.
Matt
