Hi Terry-
Here is what I did for my Vans supplied spinner and Hartzell prop. Pretty much followed the plan's instructions. Not sure what page they are on, but my 8 plans were fairly descriptive on how to get the spinner to fit centered.
I'll paraphrase:
-After making the prop blade cutouts (I used template provided by Hartzell) and installing front spinner bulkhead, I put the spinner on to where it looked centered.
- Marked the very tip of spinner with pen/marker at dead center. Hard to get perfect as it's difficult to find exact center point on spinner.
- Used a special device to hold a pencil right in front of the dot I made on the spinner. I used a step on a ladder and taped the pencil to it.
- Turned the prop and see if the dot marked on the spinner wobbled when rotating. If so, adjust spinner until it doesn't wobble, or at least get it pretty darn close. I believe the plans call out a measurement that is acceptable.
- Clamp it down when satisfied and drill bulkhead screw holes.
Regarding the overlap past rear back plate, I chose to sand down flush with spinner back plate. Key is that it's symmetric all the way around to minimize imbalance.
Good luck!