Trucks ran the wide belt pulley while the narrow belts were found on cars. The engines are identical for all practical purposes, and with the 50 engine you should have hardened valve seats which is a plus. If you bought the engine complete (including fan, generator, etc.), you can run it as is. If all those goodies are absent, you could swap the bolt on belt accessories from your cracked engine since all flathead blocks are the same (48-53 US trucks).

Check to see if the fan lines up with your radiator shroud. As long as the engine runs with no cracks or other problems, I'd say you did good. - tim