I was flying a Pulse 60 this past weekend with a Tower Hobbies 75. It has a 13x6 prop and was running 15% nitro. The plane has 1.5oz in the tail to balance with that engine. It lept off the ground and would go vertical forever. Based on the balance issue and the fact that the 55ax can swing a decent size prop, I say go for it. Prop for thrust, not speed, and this would be a real nice low wing trainer.

The plane weighed 7.5 lbs with no fuel. Drop in a lighter engine and remove the tail weight and you have a real floater.

The fuel tank is pretty big so you might even get a weight savings with a new tank. The ARF came with most of the control surfaces attached and was really a quick build. Let us know if you decide to do it, i'm curious how it would do.