I seem to remember playing this game when I put an SM 420 into my 46 Panel truck. One of your bell housings is probably for the original non synchro 4 speed. When you switch everything around to get the SM 420 to match the bell housing, you may need to check that the starter and flywheel work together and that the clutch and brake pedal assembly still bolt up to the right places. This may not be an issue for you, but I had to fight that battle with a modified bell housing. Think it was something between 46 and 47 body styles.
