The real question is what do you need an engine to do?
What plane are you going to put it in?
What is your flying style?
How much thrust do you need?
What size prop and how fast are you going to spin it?

I also believe these engine are best left pretty stock.
But which or what is stock?
There are high compression Ryobis out there.
I would like to see a Ryobi chainsaw.

A good squish band, free flowing exhaust and a proper size Carb. will wake up
most any engine with no bad side effects.

Start with these 3 things and if need be add to them.
7500rpm should be concidered the top rpm for this engine.

There are a lot of 31cc Ryobi engines being used.
Find out what you need and go from there.