Dale,
I guess AV8TOR was right about the beam mounts. That is great. I can't seem to visualize the keyed shaft. Usually you have a taper for the flywheel followed by threads. All extra holes in the case, except the pulse port for the carb must be plugged. You can tap and fit with a screw or fill with JB Weld. A carb with two needles is best. You can test it with a single needle carb. Some older carbs have a second needle recessed and covered over with sealant. If the Ryobi has good compression, it could be converted quickly for a few bucks with parts from Wackerengines.com

Dave