I use this engine in an airboat. I have done several modifications with to find some more power. Get yourself a Bowman pistonring, it will increase the compression, change the carb for one with 11+-mm venturi, widen the exhaust to at least 0.65 of bore and do NOT touch the bridge in the middle, set exhaust timing to approx 158+-, ditch the base gasket or get a thinner one to get a piston/head clerance of 0.5mm, then you will have a lot more power.

Personally I took it a little further, I widened the exhaust to 0.75% of the bore, used a exhaust timing of 162, if I remeber correctly, turned down the end of crankcase in a lathe to decrease crankcase volume, opened up the reedvalve and used 0.15mm shimmetal to make a new petal. I also opened up the transfers and matched it to the case and made a moussecan pipe. The pipe increased the rpm with 800+ or something(dont remember exactly) It turn an MAS 18x8 at 8900, and 18x10 at 7800. If you are conserned about the tourqe, start with a lower exhaust timing.

My engine was originally form a Stihl FS weedeater, but it is the same engine as the Ryobi, accept for the rearplate with the reed intake. I have the conrod on the right and the right cylinder from your pictures. Wich one is the best, I have no idea. Do the right cylinder also have the cuts in the transfers, if not I would use that one.