The weight of this bird is far to much for a 55 two stroke like the OS 55ax, there coming in at 6 1/2 to 7 pounds, that's more the weight class of a 60 size bird, this is why I chose the 91fx, well that and I paid half the price of what they used to cost new for a nearly new motor, it's never been mounted on a plane and still needs broken in.
The 91fx runs very nicely after a gallon of nitro, I have one mounted on my Great planes Extra 300 .40 the old school extra.