Food for thought, and this just my thinking:

If you have the same cowl I do with the IO-240B (I think you do) then the shorter prop might be a problem, the Sensenich
is longer. I've had better luck with the 74" prop on mine than a 72". That Whirlwind is probably too short

The cowl will eliminate part of the prop from being effective, which the longer blade helps. I'd probably start with a 74"
and see how that works.

Jeff