Real 440hp : 375hp and 480 of torque ?

A production engine was a crapshoot. If everyone from the carburetor and distributor vendors, to the machining group, the assembly group, and all suppliers and assemblers were perfect - they would be able to reach that level with careful tuning. However, the factory ratings were a little misleading. The engines were tested, max tuned for each step in the test, then the individual maximum readings were put together into one "test". This was common for all makes to do - but an engine that is tuned to make max power at 3K won't make max power at 5500.
With tolerance and quality control stacking, there were more engines below those figures than above. Careful blueprinting and tuning could exceed those figures though.