Ryan, making things complicated is apprently what I do best ... you left out overthinking things as well

.
So you just reamed the prop to 1/2" and used the spinner nut to located or center the prop. Some folks don't like to do this, but I have no big issue with it. What did you do with the spinner back plate? - drilled it out to 12mm - yes.
Also, if there is plenty of thread left for the spinner nut then I can use the TT-0100-A adapter (pic below). This will eliminate the need for the counterbore. Then it's just a matter of reaming the prop to 10mm.
Moses