Ahhhhhiiiieeeeeeee, I think that the hard tops lock everything together. You might be opening a can of worms, if your lower windshield seal doesn't leak now, oh - right, you'd want to angle it tward the rear, so it might tighten the seal. When I took off my top and back, I noticed upon reassembly that there really isn't any available play forward and aft with the top at the windshield and where it meats the back. You'd also want the tops bottom edge to line up with the back vertically. This windshield adventure unfortunatly won't help the windows flapping outward. Maybe its designed this way, to act like skegs on a boat to keep the truck tracking straight down the road, (seeing how fast they go, they might need the help)!!
I just looked at the angled flaps on the top (above glass) and the vertical angle flap on the back. They meet at a 45 degree angle. Once this joint is tight you can't move the windshield back any more. The top will slide back on the back part until these two pieces touch and thats it.