Duster 340 not a muscle car...

Best 340: the 290HP Six Pack. (Note the 1967-69 Z/28's 302 matched that.) Best muscle-era Chevy 350: the 370HP 1970 Corvette LT-1. (The identical engine was rted at 360HP in Z28's.)

I would not believe Chevrolet rated HP numbers. Look at NHRA numbers.