Back in the '70's and early '80's I did a lot of engine work on controline, Free Flight and racing engines and I had a test stand that I made onto a piece of pipe that I could drive into the ground. I didn't live far from the airport so I would go over there when I needed to run an engine. I tested a LOT of head inserts with different combustion chambers and learned a lot in the process. When I started running boats in 1985 all of a sudden I had a tuned pipe and a throttle to deal with. Many of the boat engines of that period had an equivalent airplane engine. At that time I was running Picco .45's in D mono and Picco .21's in B mono. I simply exchanged the flywheel for a drive washer for the propeller and propped the engine for the RPM that I wanted to run in the boat. To run the .45 I had to turn the case 180 degrees so that the exhaust came out behind the prop. To operate the throttle I used a piece of wire with an "S" bend to attach it in the throttle arm and rubber banded it to the base of the engine mount. I could set the throttle anywhere I wanted it to be.
Your set-up to mount the propeller would be MUCH safer if you got rid of the collet, flywheel, etc. and got a regular airplane drive washer, washer and a nut ( I'm sure Glenn could find one for you ). I would also get rid of the wooden prop. Anything over 20,000 RPM you could shed a blade, and you don't want to be around when a blade comes apart! Get a good composite prop like the ones that APC make. I don't know what these engines should RPM at, so again, ask Glenn and then you will know how to prop the engine. My guess would be an 8X3 or an 8X4.
I will agree with you that this is a great way to break in an engine. You have to be careful around the prop, because it will hurt you if you're not.
Dick Tyndall