I think the big tires can add some clearance for a 13 x 8 three-blade prop, which I am sure an engine like the 75 AX could drive without much difficulty. It may be the best compromise between clearance and air movement. Be sure to consult with the manual that comes with the engine, as for a 3-blade you'll step down an inch in length and pitch. Besides, I am sure the plane will look better.

NorfolkSouthern