Interesting, I was thinking I saw somewhere here that the motor mounts for a '54 were angled. I guess the bolt holes for the flywheel cover are the only real differences. I have a bell housing sitting in my garage with a casting number of 3701433 which translates to a 48-53 truck, with the flywheel cover slots spaced at 9-3/4", and has vertical motor mount bolting.
But the one on my truck is the same casting number as yours, so is a 1954 as well. The motor mount holes are vertical on it like yours are. That kinda makes sense, though because the engine was swapped back in 1954. It's not readily available to measure the bolt spacing, but there was a correctly fitting flywheel cover with it when I bought the truck.
