GM Experimental Prototype SBC 3x2 / Tripower setup

[William]

That was to be the L70 350 option for 1967; it's shown in the 1967 Assembly Manual. Cancelled April 1966. A few '0-' manifolds are known to exist.

If Smokey Yunick had anything to do with it he didn't mention it in his book. Since Chevrolet cancelled it long before introduction day I doubt it was ever considered for the Trans-Am. It is not listed in the SCCA Homologation papers for the Z/28.