The Rochester Monojet was a 1 barrel downdraft carburetor used from 1968 to 1990 on 4 and 6 cylinder engines.
The first version was the MV, which used a manifold mounted choke thermostat with an integral choke pull off diaphragm, and the model M, which used a manual choke.
Chevrolet truck 292 CID Rochester 1MEF carburetor
The model 1M (1MV with automatic choke) was a revised version in the early 1970s. An electric choke version, 1ME, appeared about 1979 and was revised in 1986 to the 1MEF model, with an adjustable air bleed. These were used exclusively on 292 CID engines in trucks after 1979, along with the 1M manual choke version. Model 1M carbs were also used on industrial engines (forklifts etc).
Carburetor numbers were stamped on the side of the float bowl.
Rochester carburetors listed by carburetor number