G'day again.

An OS 46AX is about the equivalent of a 60 size four stroke. So, if you have a Saito 56 in your Mustang, then an OS AX 46 (or FX) will be about equivalent. It partly depends on the type of plane you have. In gereral, Saito engines are more powerful than OS four strokes. There is a graph of this around somewhere here at the moment.

You did not say what sort of engine you have that is damaged or needs repair and you did not say how big the model is and both facts would help. If you have a 40 size Mustang then the AX will be fine. The LA 46 would be a bit marginal.

More details will get you a better answer.

You can put much bigger engines in planes than they need and they will fly but beyond a certain size, all you get is more noise and more fuel consumption and more weight and none of these is worth having.