On the Chevy II departure for 1967 my guess would be that the L-79 was removed from the ChevyII due to power to weight ratio concerns. Curb weight was only about 2900 pounds with the V8 in the 1967. The motor was approved for return in 1968 with the Nova redesign.

On the Horsepower reduction, the smog up of the L-79 was a direct result of the enactment of the 1966 National Safety Act which required smog by 1968. As a result of the emissions controls the HP dropped to 325HP.