I would measure the actual radius that you have before attempting to find a solution. 1:10 would be a fairly aggressive radius. You could mill a teak box which holds the hatch flat and square on the top and is milled to follow the radius on the bottom. Similar to the box the dorade is mounted on in the pic from RTF in post #8.
Honestly, if you have the front window open all the way and the side windows open, an overhead hatch probably isn't going to do much for you. The only benefit I could see is I don't like having the windshield open underway, so the overhead hatch would help that issue, though again, with an openable side window, I'm not sure how much that will help.
I'd be concerned that the amount of labor will far outweigh the benefit.