An idea for being "sure" you've measured thrust....Go to your local Builders' Square, Payless, Home Depot, etc, and buy a piece of 3/4" angle aluminum stock..1/8" thick stuff.  Cut a length at least 20" long.   Mark the center EXACTLY, then drill VERY carefully a clearance hole for the crankshaft on the 90 degree corner.  

With motor mounted, and spinner back plate installed, place the alum bar with the "point" of the angle facing forward, install a washer and prop nut. Rotate the bar exactly horizontal, measure tips of the bar back to whatever reference point you choose.  This is also helpful for checking wing/stab alignment horizontally, as you can reference up to the horizontal bar.

Rotate 90 degrees to check up/down similarly by measuring back to fuse centerline, stab, whatever.....

This works.  

Bob Pastorello rcaerobob@cox.net