Per Dean Hoffman:

Would something like a chain Vice Grip make a good handle to help turn
the antenna? Harbor Freight sells a less expensive version.

I have a couple of strap wrenches and expect (?) them to do the job.

I'll put a little PVC pipe sleeve in the top bracket so rotating does
not score the mast and tighten the bracket just enough to prevent any
side-to-side movement, but not enough to prevent rotation - although
rotation will not be that easy.

Then I'll tighten the lower bracket enough to prevent rotation.

Might do the PVC thing too if I can still tighten enough to prevent
spontaneous rotation.

Come re-aim time, I'll loosen the lower bracket use the strap wrenches
to rotate to taste, and then re-tighten.
--
Pete Cresswell