brownie1,
There is a block casting number to the right of the starter (most likely: 3701481, 3702436, 3835911). There is also a head casting number on the distributor side but it is not uncommon for a different head to have been used over the years of service.
Several people on this site have a 1954 1/2 ton with a Hydra-Matic engine. F54M indicates 1954 3100 series (1/2 ton) with a Hydra-Matic transmission. Why do you think that engine serial number has to be a rebuild number?
I bought a 1954 Rochester carb for an 1954 automobile from Auto Zone for under $70 (for my '54 Hydra-Matic). It had the automatic choke set-up to work with the a tube from the choke mechanism to the heat stove on the exhaust manifold. Do you need the tube?
As far as rebuilding the engine, this engine is not really any different for other 1954 235 truck engines. Some people think that checking for a local rebuilder is a good idea. That sounds good, but I would ask how long ago they last worked on a high-pressure 235 and from whom would they be getting their parts. Also, ask them if they have a Shop Manual; if they say they do not need one, I'd be wary. You should buy a 1954 Chevrolet Truck Shop Manual, if you do not already have one.
If you want a deluxe rebuild and money is not much of an object,
Jasper Engine & Transmission has an excellent reputation.
Good luck,
Tim