You got that right.
When you lower the lid, the tumblehome increases. The roll-down windows track moves outward at the bottom, balanced by the fact the window is shorter.
I'd cut across the bottom of the windshield (through the windshield wiper area)and lay the windshield back, then fill in the gap that opens up. A slant chop will put the back of the roof where you want it to be and save having to cut the DOT-approved windshield.
The rear quarter windows can be plexiglass. The door windows could be plexiglass with a hatch to hand over you license and insurance (or receive your timing slip
) through. In the back you should have a massive boat tail anyways.
Polycarbonate Windows Race/Track/Road Golf GTi Championship Approved Supplier