ORIGINAL: DougT
Bob,
I've been running the Gen II. for a while now and am fairly happy with it. CH ignition makes it idle awesome and the sound is too cool. BUT, I did mount it inverted for exactly the same reasons as you and lost about 1000 rpm and the idle was not reliable. It also wanted to puke out some of the oil from the case breather tube. I understand that the Gen III have the breather on the valve cover. Is that correct? It may make inverted better or worse. I'll take a head-on pic of the Ryobi with a height and width measurement and post back here.
Check out this. I want to start building it this summer. The main holdup is milling the crank for it.