Correction - The GD hardtop includes
gullwing windows, not the whole door, and it appears to also incorporate the windshield frame like your top. Pictures are difficult to come by but you can see it here:
www.gdcars.com/assets/brochures/Mk3.pdf
Its quite likely you are already familiar with Gardner Douglas (correct spelling) but if not, check out their website - you may find their backbone chassis and body mounting system interesting.