Hey Bud,
Changing 'props' is not the question; Changing engines IS!! But also comes the problem of the SIX inches from the firewall to back of the spinner on that aircraft. That kind of limits your choice, unless you don't have a problem 'cutting the firewall??
The O.S. 160 is a great running/power engine in its class....for nitro. I am considering going GAS for that aircraft, but the six inch firewall to spinner/plate IS the issue. You can go with a new 2.15 gas (35cc)Mvvs engine on 'regular mounting rails' would be good too. I was thinking BME 44cc can clear a 20" prop 2 blade, 18" three blade, OR a /BME 50cc gas, wants a 20-22" 2 blade, but also a little heavier. I think the goal for engine weight will be ~ 3lbs. To Bad BME hasn't released the new BME 55 Extreme yet, that thing is projected to come in @ 2lbs for the engine + 1 for the muffler!! Trying to go with the NEW 50cc gas engines i.e. DA, 3W(24cc, 42cc,50cc) is a little more tricky because they are rear inducted AND you'd have to custom-cut the fire wall to fit!! AND both are not the lightest in the class, but probably the smoothest running!! Also, what kind of flying are you planning to do with it....OS 160 can do most things well @ 3-4 hp....I WANT '5' horses!!
I'd still like to know; "HOW BIG A PROP CAN YOU CLEAR WITH THE STANDARD WHEELS IT CAME WITH"...with a couple inches to spare!!????

Sincerely,

PanchoBiplane