"Does anybody have exact measurements that can be given to a fabricator?"
Would suggest that the fabricator will be on your
boat doing his own measurements, then if it does not fit his issue not yours.
The width will depend on the
panels. They will probably tack weld the upright to the plate on top then take away to fully weld and re-polish. The drawing you have with some basic dimensions will be a good start for getting a quotes.
Now is also time to think about a means for lifting
outboard on to
deck if required. We hang a sun shade off the
solar frame to shade rear
deck at
anchor. Good luck and enjoy the journey.