ORIGINAL: microsprint9

That looks like a good conversion engine, as mentioned above cut off all excess aluminum and i too would grind down those tabs on the back and use the 4 backplate bolts to mount it. Your shaft on that engine is just like mine, all what i did was cut it down a bit and rethread the end and for the prop driver all i did was take a pc of 1" aluminum rod with a 5/16" hole drilled thru it and used a nyloc and washer to attach the prop. I wanted mine lite and i too was worried about interferance so i went the GAS/GLOW way, this saves lots of weight as you can remove the flywheel, coil, and sparkplug, and the best part is no interferance as the engine runs off a 4 stroke glow plug like a normal glow engine. Here is my weedeater 21cc conversion.

As for props i was using a TF 16x8 @ 6900rpm and an APC 17x6 @ 7200rpm.