RE: another darn ryobi post (ryobi performance modification, analysis and comparison)
Jag engines and others make mounting kits. They look heavy however. I just use a flat plate with a hole in it for the carb. It is mounted to the back of the engine, on top of the original plastic backplate. You then use bolts and stand offs to mount the engine. Note that you need to make a spacer about 3/16" thick for the carb so that the linkage will clear the mounting plate.
AV8TOR