Received new antenna. Came with nothing but a base gasket.
Determined I had 8-32 machine screws and nuts, so I was good.
Cut a piece of .060" backer plate and drilled it for the holes in the antenna base. Attached a 5' length of RG58 so I could test a used comm I purchased.
The antenna has a pretty fair amount of fore/aft wobble due to oil-canning of the fuse skin. You can see the gap at the aft of the backer plate. I've determined I'll run a section of L-angle from the aft of the backer plate to the diagonal stiffener about 8" away to improve the rigidity.