take a close look at the factory position of the throttle shaft............ for me a pain getting alignment going aft. (This position thing may be all wrong, I thought this was a homelite engine.)
Dave's suggestion to make a new makes sense to me. Have the material just haven't done it yet. First attempt was making an additional twister plate of alum. and that added needless weight.

Are you using a stud in the front part of prop hub thru the prop and threading into the alum 'spinner nut'?

Loose the centers of the mounting bracket/plate...

Which version? http://www.donsmithplans.com/

Have you searched thru Engine Conversions for info? A lot of data and tips.