Sorry, don't mean to be difficult here. There is something that just doesn't quite seem "perfect" with the proportions in that photo shop design (though cudos for the effort). I will say the roof design shown has potential and further "sketches for refinement" are definitely warranted (and I have a feeling professional auto designers in the real world do nothing but that, "all the time.")
I am going to pretend I am an auto designer just for the moment. As it is, in attempts to refine the roof design in my head, say, raise it just a bit, then it starts to remind me of a Jag E type. If I envision tapering the rear, it starts to remind me of a early mid 60's Vette. Ok then, maybe not tapering so much to a tapered point, maybe a little bit truncated. Then it reminds me of a Crossfire.
I think the design as Turney photo shows does look more appropriate given the style of the Healey as it was originally designed in the 50's (and carried over well into the 1960's). The hardtop design that came with the Healey during production still stands as true and aesthetically correct to me.
Again, just my opinion, the sloping roof line as Healey Rick's pic does have potential. But as you can see from the side profile, it has a very slightly 'heavy' with an elongated appearance. And the heavy look could be the result of the fender curve designs as they currently exist.
Maybe just adding some accents like what the Vette had or include subtle vent cutouts like the mustang fastbacks could make it more interesting. Otherwise, I tend to believe one should just start all over again, from scratch, at the drawing board. Saying that is a good thing, too, for I believe Donald Healey did a fine job with this car. It really needs no refinement.