The 500 motor is almost 4 feet long, though. It IS about 6 inches narrower than a BBC but the exhaust will take up some more room on the side, eating some of that back up.
Height is short, but it's fat at the bottom instead of narrow like a v motor.
Weight is only slightly lighter than a BBC, and fuel usage is 35gph at 325 hp (a bit thirsty, as most rotaries have proven to be).
It's obviously got room for tuning for more power and swapping to gasoline.
But where would the rumble come from??
Can't have a muscleboat that goes: FzzzzzzzzzzzzzzzzzzZZZZZZZ!