Chook,
The spinner problem is a real b***h! I contacted the Tru-Turn people for their help as I need to mount an 18" prop on the RCS 140 gasser. The hub area is so large the the cutouts are, by necessity, almost too large for this size spinner. They recommended going up to a 2-1/2 " size instead of the 2-1/4 in. which comes with the plane. Those folks cut one for me to fit the Windsor Classic 18 X 6 prop. This slightly larger diameter spinner looks very good on the plane, but is very minimum for a prop of this size. A 16 inch prop is noticeably smaller in its hub dimensions than the 18 inch if you can use one.
Hope this helps!

Sam