I don't know Tim, good question. '41's didn't have the flare so maybe they were the same as a car. I never really understood why there should be a difference in the hinge. I can't picture needing a heavier hinge for the trucks?. I guess if you were going to be hanging on it like a monkey, it might last a bit longer, but would still probably bent the door frame or something?. The narrower hinge could have been done just to accommodate the flare?.
I just got a '42 C8sd., and I think I am going to check the width of the lower door hinge. I'll get back with that result.