M4M (1975+) quadrajets for 350 and 455 were based on 800cfm castings. They had different dead stops on the air flaps, limiting the max airflow and thus "cfm" of the carb according to the particular application. Jetting was different for each as well. so yes an "800cfm" qjet can be used on a 350. As was stated above, the important thing is that the carb be "set up" for your specific combo. IF you were going to take a generic stock 1971-1974 Buick 455 800cfm quadrajet and put it on a 350 it would work well, with the possible exception of a bit too much idle air bypass. Youd end up backing the idle mix screws out a few more turns and closing the throttle angle a bit too.
