"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
. Good luck and enjoy the journey.