Whatever angle you make your arbor/hub taper joint, check your accuracy by printing the fit of the arbor back to the flywheel with some Prussian Blue or just by using pencil marking or chalk. That way you will know how accurate you are? But remember that your arbor is harder than the flywheel so be easy with trying your fits so you don't mark the original flywheel to the point to where it is inaccurate.

When you get your new hub turned, you can check it against the taper on the crankshaft this way.

Also, if you make a aluminum hub, and after checking, you find a high spot or slighlty off angle condition, you can lap the hub to the crankshaft with some fine valve grinding compound. Also some Locktites will fill voids that are several thousanths.

From my experience, on Homelights, The long shaft engines have a 3/8" shaft and the short shaft ones have a 5/16" shaft. The taper appears to be the same angle on both sizes but, of course, the long shaft version has a larger diameter taper. I found out the hard way that a long shaft flywheel will fit a short shaft taper but it goes too far up on the taper for the mag to work it's best.

I've seen different angles mentioned for flywheel tapers that are anywhere between 4 degrees and 5 degrees and 43 minutes. Notice that this is half the angle mentioned by Ron but this is only a matter of terminology of thinking about both sides I believe?

Good luck and enjoy,

Jim