My 55AX works just fine with a 12-6 prop, and one of the recommendations in the owner's manual is for a 13-7. You should be good to go with your setup. I'm thinking, that 13-6 might add quite a bit of torque, so you'll want to manage that throttle while taking off. A 12-6 would offer better ground clearance, while power should still be more than adequate for that Decathlon. This engine will pull stumps just about as good as any old John Deere tractor. Trust me.

NorfolkSouthern