On the right side of the engine, just to the rear of the distributor, there is a flat machined pad with a number stamped into it.
The first three digits represent the engine displacement. It may be a little difficult see with the distributor shield in place.
Can you post a pic of the metal plate on the left side of the engine? If it is an arsenal rebuild, it may say where and when it was rebuilt.
It is almost definitely the military version. Features like the distributor shield, the wide pulleys, and the cast iron Zenith carburetor are unique to the military version of this engine.
Best Regards...
