yeah, there was exactly what your talking about out professionally a while back... actually my local friend, Wraenking in here, has one on his K5..
on a separate note, I should post that rig for sale in here, he called me about that a couple months ago...
anyway, yeah, black vinyl that slops kinda to the tailgate.. it has a little isenglass style window up near the back.. it doesn't actually straight slop from the roof, but kinda goes down, than back..
to be honest, I thought it was pretty butt-ugly.. but obviously it's effective for what it's intended for.. I've seen a couple turn up in here over the yr's, but not many..
we also had a guy a few yr's ago that did exactly what your talking about.. don't remember who, maybe if he's still around he'll chime in.. his was a lot more "flat" from the roof to the back.. I kinda liked it better than that pro one Tom has...
usually dealing with, making up, the "bows" for the softtops is the most difficult thing for people to come up with (tho it sounds like your design wouldn't run any...) and should be pretty simple for him to make up.. some snaps, couple rails, yada...
I have the ultimate "in" if I ever wanted to make one being a marine guy with a bunch of canvas guys at my disposal.. the bimini top bows on boats are ideal materials/construction for a softtop...
but I jumped on the fastrack when it came up... it was dirt cheap from a good mod here on the forum.. $250 and it was pretty perfect.. other than a few factory issues I need to work out with my canvas guys when I get the rig running...