I'd suggest watching all the videos from The Arnold Company. Start with "Why It Goes So Fast" and pick your flavor from there. After his death, his family released all the videos to You Tube. They were originally only available by purchase. Link here: https://www.youtube.com/channel/UCVDILmX2ylWP1YLQmYi9nPw
Over kill for an Avid Flyer or Kitfox but worthy of mention is the solution used to fix the tail on Draco. Link here: https://youtu.be/j2WKyra8HBc A small air cylinder with adjustable flow ports on the intake and exhaust could be used to dampen the Avid or Kitfox wheel similar to how the Draco was tamed. We had many hydraulic cylinder designs that used this idea to control flow under various load conditions. Those smaller air cylinders are made of aluminum and are very light and the flow restriction idea works for air just as well as hydraulic fluid. The gas block on an AR-15 is another example of a port being used to control gas flow rate. Many applications use needle valves to make the flow rate adjustable.
The gearbox can be mounted in four different positions. Too bad nobody makes an intake manifold to fit a down draft carburetor on the Rotax engines. Then it could be mounted on it's side with the intake on the top and the exhaust on the bottom. Any fuel mix dripping through when it's not running would drop out the exhaust ports if it happened to make it past the rotary valve.
Once you add up the parts, your right, the weights are very similar. I do like the idea of getting away from two stroke oil. The people running them in the past seem to have almost as many problems as people running 2 smoke engines. http://www.teamkitfox.com/Forums/showthread.php?t=7745 I'm sure if I had one laying around I'd have to try it. Price wise they seem like more money without any savings in weight, fuel consumption, or usable horsepower in Avid Flyer type aircraft. A reduction unit would take advantage of the extra horsepower but then your taking an additional hit in the weight department. Their website lists propellers for their engines and there are none longer than 60" and that will restrict performance in our style aircraft. The lower R.P.M.'s is something that should mean an engine that lasts longer but it has not been working out that way.
I had downloaded that a while back but find it very over simplified. For instance they recommend the 6500 rpm and give no reason why you would static load it to max. horsepower. They also recommend just clipping off the ends as good enough for balance. I don't plan on cutting mine off but if I did I'd be at least performing a static balance. Maybe they do this because most people don't have the tools I do to make a precise centered hub balancing jig. They also say nothing about checking blade tracking. That's something a little harder to correct if it's off because of the way the propeller is designed. Back when Ivoprop first hit the market some of us that were flying Mitchell Wings wanted to try them. I'm glad I didn't. On a Mitchell Wing the prop clearance between the propeller and the trailing edge is only a couple of inches. The guys that tried them found out the hard way that the Ivoprop flexes under load and it chewed up the trailing edge of the wing as well as the propeller. Being a metal wing shell laminated over a foam core made it a touchy repair. Mitchell Wing notified people not to put the Ivoprop on the Mitchell Wings but people buying them second hand don't always know these things. Anyone here remember seeing the propeller cross section displayed at Oshkosh back in the beginning besides me? The core was made out of blue foam back then. (Maybe they still are?) It explains why they flexed so much.
I'm guessing it works like a guitar tuning peg; if you go too far you back it off farther than you want and then tune to prevent it from drifting? Boring heads on milling machines work the same way and you can't back them off of tension while setting them.
I need to set it to something before I can tweak it into the power band. I won't be messing with it until spring at the earliest. The older I get the more I hate winter. I got rid of the snowmobiles a couple of decades ago and I only snow ski about once or twice a year anymore.
You mentioned earlier that it climbed like hell; what gear ratio in your B box and what pitch is that Ivo set at? What kind of cruse are you getting at those settings? I've got the same prop but will be running it on an Avid Flyer with a 582 (same horsepower) with a Box geared at 2.58/1 and need a starting point for pitch.