My first ryobi is on an 85" Stinger and of course is underpowered.
The plane flies real well at slow speed and is fun to fly. I have a 16-10AS classic turning 7500. The jug is the slitted variety and it is a single ring piston. I know there is a lot of room for improvement and my question is where first? prop? dual ring conversion? unslotted jug? opening reed valve limiter? muffler mods? or just go fly? One of the fascinating things about the ryobi is that there are a lot of options to experiment with which is what this hobby is really all about to a lot of us. Where do I turn to for conversion parts?

opening the reed valve limiter to allow an 1/8 allen wrench to slip under is only your labor.
I did this at beginning, so can not tell how much if any it helped.

Put dual Bowman rings in non-slotted head and changed it back to duals in slotted head, as I could not start it with tower h-d starter without loosening plug for compression release.

If you have the ground clearance, try a bigger prop. I feel the ryobi does better with torque than higher rpm's.
I run an 18x10 on mine at about 6500 rpms. This is a basically a stock motor. I ran the numbers against your 16x10 and it's nearly 2lbs more thrust with the 18x10. An 18x8 would be worth a try as well. The APC props are leaps and bounds better than others I've tried in this size range. You will notice a difference. The added thrust , even 2lbs, can make a so-so plane a pleasure to fly.