John T said:

Really good! I'll have to make one of those, nice and simple!

Thanks, John. I haven't seen one quite like it on the web, but I was
certainly impressed when the first 12 wedges went together.
Total cost was: $3.60 for a clamp (on hand) and some scraps.
(And a few days of mulling it over in the back of my mind...)

If you cut too far on one boss or the other when aligning the mitre,
it may be shimmed back up with HD fabric or vinyl tape. This would be
done so that the top mounting screw registers properly - the
clearances on my holes are pretty tight.

FWIW,

Greg G.