Need help NON mopar 1967 Pontiac Lemans 326

Yeah, typical GenericMotors move, that was one year only from what I can tell....chuckin' the Chebby 307 in there so they could use the same trans as the 250?
Anyway, this isn't the OP's problem, bad plugs/wires(even if new),or a flat exhaust lobe are more likely by the sound of it.