But weren't they a Yenko car, not a Chevy factory delivery? Didn't Yenko Chevrolet put the tweaked 427 in the car?
From Wikipedia
1967
Yenko ordered L-78 equipped SS Camaros and swapped in the Chevrolet Corvette's L-72 427 in?ウ (7.0 L) V8. The cars came with a 4.10 rear end and heavy-duty suspension. The exact number of cars produced is not known; most estimates are around 50. Yenko also installed a fiberglass replacement hood similar to the "Stinger" hood featured on 1967 big-block Corvettes.
Don Yenko's Camaros were equipped with a 427ci L-72 in them with either an M21 or M22 transmission. The horsepower was rated at 423 hp (315 kW). Yenko Camaros were not allowed to race for Chevrolet on the drag strip because they were not made by Chevrolet.
I think the fastest were the Hemi Cuda's of the late 60's. But, they were not street legal...
That was the difficult part; Ford was next fastest to Mopars. Then GM. UNTIL... NASCAR, NHRA ect started restricting the Hemi's so the other manufacturers could compete.