Given the variation in Morgan body tubs, I wonder if a Targa-type arrangement might be a solution, with a rear section that bolts down to the tub, and removable roof sections to bridge to the windscreen?
To my mind, the big drawback of a conventional hard top is that you can't easily remove it if the weather is nice, but with a Targa one could whip out the roof panels very easily.
Getting it to look right might be a challenge, though...
...what used to be called a Surrey top. Very popular on Triumph TRs