I got it (I think). I had my wife help by turning the prop as I moved the throttle through it's range to try to find neutral. I had to remove the handle (spline nut not in place) to reposition it to get the full range. When in forward, the prop will lock in the counter clockwise rotation and in clockwise when in reverse (it was 2 days ago so I think I'm remember the direction correctly). So, if it was locked in one direction then I moved the handle toward the other position until it was free in both directions--that should be neutral. Then I remove the handle and placed it in the neutral position on the spline. It took a bit of maneuvering but I think I finally found the correct neutral and then verified it by taking it out of neutral in each direction to make sure the prop rotation locked correctly in each direction. It seems to have worked. However, I don't want to fully test with motor running until I get the replacement center neutral button. It should arrive Wednesday. I also still have some cable tie screws to install, etc from my re-carpet job.
Lesson learned here is, if I ever have to remove the throttle handle again I need to take a photo of the position before I remove it!