Kevin,
You have two choices with the crank shaft on gas/glow. You could make or have made a prop hub that slips over the 10mm rear shaft, using a bolt and washer to retain the prop. Or you could cut the center from the flywheel and install it in its original shaft location. Then purchase a screw on prop hub. The hub would seat firmly with Loctite, against the trimmed down flywheel hub. This would be the easiest way. If you decided to use the slip no hub, it would be helpful to take the engine apart and reverse the crankshaft. The slip on hub could be cut for the key, if desired. I find this fairly eay to do with a swiss file on aluminum. While you had it apart you could trim away the old flywheel housing, making it lighter and more compact. The undrilled flange on the case by the straight shaft would need to be drilled for either direct mounting or a mounting plate. If you decide the take it apart, you can use a Dremel tool with a cutoff disk to remove the unwanted portion of crankshaft. If you cut the shaft with the engine assembled, cover all ports and openings with tape to protect the inside of the engine. Do not allow the shaft temp to rise to much, or you will damage the rear seal and have to replace it. The hole above the exhust port, if it goes through, into the cylinder bore, it should be plugged. This can be done with a screw. It may need to be threaded. I use a 10-32 tap and JB Weld to secure the screw. A 10-32 is a good match for many of the metric bolts used to hold the engine together. My favorite glow plug adapter is a Zenoah, available from Horizon for $9.95.

Dave