PeteCruz, I don't have a photo yet of my manifold heater door hole, but it is a very LARGE one in the firewall, just above and in-line with your exhaust manifold. About 2-1/4" diam. Up here in the Northeast, I can count on one hand, how many A's I've seen that DON'T have that heater door hole. That's restored ones, "woods finds" and everything car in between. I like the idea of a water heater, but the "A" has such limited room up front for the heater core and a real pain to remove the floorboards sometimes if all the floor screws are in place.