A lot of what engines you may use depends on what you want the plane to do.

A 60 2 cycle glow engine will pull your Joss Stick around the field but it will be rather disappointing as far as waht it will do because of a lack of power.

Your original idea of a .91 2 cycle would be a much better choice.

There is a lot to be said for the newer design 4 cycle engines for this plane. The Saito 100 or Y-S 91 FZ would be modern - day light weight choices that will give you the advantages of 4 stroke power.

The only other Joss Stick I was around had a OS 120 4 cycle on it and there was nothing wrong with that combo.

A Zenoa 26 gasoline would work nice on one too. But keep in mind that you would probably want to mount the servos in the tail to offset the weight of the engine.

The stock Homelight 25 would fly it about like the 60 glow engine. But a Homelight with the G-23 or 26 carb on it might be interesting.

The Ryobi gasoline engine is rather long and unless you shortened the nose by 3", you would have a hard time balancing it.

If I were you, I would pretty much ignore any horsepower figures that an engine maker quotes. For as you may have already noticed, they are based on unrealistic rpms. I decided that some 45 years ago and I havn't changed my mind. I don't understand why they even bother? More realistic would be a certain prop at a certain rpm with a certain fuel, at a standard temperature and pressure. That would be more like it.

Enjoy,

Jim