Jason, it will start just fine once you make the shaft. Be sure the allen bolt is loctited solidly on the engine, since it is trying to unscrew itself during starting.
You should be able to make a shaft by using some a 1/4" rod or stiff tube (like stainless steel brake tubing). It would be nice to have a coupler machined to secure the hex key to the shaft. If not, perhaps you can push the hex into the tubing and 'hammer' the tubing into shape. You could secure it with a little epoxy too. Or you could adapt some brass tubing to do the job.
On the other end we've have used a normal prop spinner for the starter cup to engage.
Of course we used brass tubing on the outside of the shaft to hold onto during start. Put a little dab of grease on the hex end too, to minimize wear.
I'm sure there are other ways to do this as well. Good luck; that .46 is a fun, strong engine.
Jim