Yes Ethan1 your right , the 7040268 was for the 455H.O. and the 7040270 was for the 400RA IV . Could you take a look at the front cover of Cliff's book and tell me what you think the carb is ? I think it's of a Buick GSX 455 Stage 1 . What numbers were used on those carbs and what were the internal specs ? How much different were they from the standard Buick 455 carb (auto) ? Was the Stage 1 option only available for 1970 , 1971 & 1972 ?