I'm not sure I understand the cloth top, like a sunroof? or a roadster pickup?
I don't think I miss the opening windshield as I have a louvered hood and alot of engine heat would be coming in. I even took out the cowl vent for the same reason, and yes it gets pretty warm in the summer. The joys of hotrodding.
You have hit on one of the big problems for me with the none framed door glass. I've broken mine several times because there is not enough down in the door to hold the glass, to keep it from hard shakes. My glass guy is one of the really good guys as he offered to replace my broken glass the first time for free. I paid him anyway, and have not replaced the glass yet this time. I have two problems, one was that when I first took my doors to him to cut glass I didn't take the inner window trim and after installing them the glass is not lined up with the guides as well as it should be (my fault not his). The second problem is that there is not enough guide inside the door to hold it tight. Both of these problems are going to be fixed by taking the complete doors back to him for a rebuild as soon as I can.