There are a number of details in the pics that you have provided that screams car engine to me.
1) Does that engine have a carburetor with an automatic choke? If so, that carb came from a car.
2) The down draft tube has an extra wide bend in it so that it would clear the threaded side mounts found in cars.
3) The vacuum advance is clocked 30-45 degrees toward the fender. This was done on cars to also clear the side engine mounts.
4) One of your pics looks like someone put the bolts back into the holes where the car side mounts used to be.
5) That blue paint has been on there for a very long time. That looks to me to be the original color used on '54 car engines.
If one were to ignore all of the factory documentation provided to indicate that it is indeed a car engine, the only way to continue to be convinced that it is actually a truck engine would be for one to assume that at some point, someone pulled the engine, removed all of the above mentioned truck parts and replaced them with car parts and painted the engine blue a long time ago.
