RE: prop size
What's the biggest prop you have room for?
I have a pair of 55AXs on a B-25. I finally settled on 12x6 MAS 3 blade props. These let the engines turn about 10,500 rpm on 15% Cool Power, good for around 60 mph and gobs of thrust. They never liked any of the various two blade props I tried, including the ones recommended by OS.