Can anyone here tell me how many cfm of air I need to move to safely run a 300 hp diesel engine inside a 4,100,500 cubic foot facility?

The solution is not dilution.  You can seriously injure or kill building inhabitants.  

Exhaust should be routed outside of the building in an area that prohibits entrainment.

Check your ASHRAE standards for details,

ACGIH for exposure limits to CO & NOx

Fixed?  Pipe the exhaust outside.
The 400 Hz generator was a monster.
It was a diesel.
Had a 4 cylinder gasoline engine to start it.
The 'starter' had a battery system t start it.

When it failed after a good 50 years of use, a NG turbo generator replaced it.

Mobile?
Keep the doors open.

If we needed to run a plane engine to work on it in cold weather we put the tail a few feet outside the door.
When the weather was warm (or hot) pull it out to the flight line.

Air Force Plant 42 is in the desert so it was usually hot.
Site 2 was SR and U-2.

The SR engine test stand was at the far end of the flight line.

That is how we did it in hangers.