The main differences in the different years is the mounting point of the canister. Tim, when did Chevy move the vacuum port to the "Box" necessitating the move of the canister to the front intake rail? Since the 40-47 schematic shows it on the front rail I'm assuming it was in '40?

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.