I got my centrifugal clutch kit from ZoomCycles, too. It came, like, yesterday.
I have found that the tapers on the crankshafts vary from engine to engine, loose sloppy tolerances, etc. I test fitted everything on a spare crankshaft that I have, and it fit perfect, then when I tried to install it on my regular MB, it stuck out too far from the end of the crankshaft and rubbed against the outer cover when it tried installing it.
I machined away most of the taper on the clutch and also machined a keyway into it so that I could use the Woodruff key from the stock gear.
It slid on nice and smooth, and took in the little bit of taper left when I tightened the bolt down.
There are other posts on this forum writing about how the taper-fit clutch assembly has spun on the crankshaft, thus wearing away the taper, so right away, I modified it for use with the key.
As of now, I have put 50 miles on this setup with zero problems.
I like how it works, and from now on, all my MBs will have a centrifugal clutch on them.