Not so much a resonant tuning. but more likely a pumping efficiency optimization. Every IC engine, whether it is the Otto cycle gasoline engine or the Diesel Cycle, well, diesel engine, is essentially an air pump, whose efficiency depends on many factor: CR, port timing, intake & exhaust plumbing, etc.

What Duke Fox found was probably a crankcase volume at which that particular combination of engine parameters resulted in the best pumping efficiency.

If you got gobs of time and patience on your hands and don't mind the possibility of gaining zilch in the end, then by all means experiment. Power gain is possible but by no means guaranteed.