Cutting out the T-bar w/out extra rigidity added to the A pillar assembly is a serious issue because the A pillar will fold back if struck at all.
As for the rigidity of a FACTORY Ttop car they have extra bracing that a solid roof car does not. The factory Ttop cars have a structural bar built into the Bpillar and roof that adds a Structural hoop that the Tbar ties into to hold the A pillar forward. The other part is that on all modern cars (ours included) the windshields are glued it because they are designed as a structural part of the A pillar section which allows even loading of forces. As for twist in solid roof vs T roof models that is a lack of improvements by the owner/buider because in order to severly twist the frame you have to increase HP/Torque output to above vehicle engineers design. Like any modification every part has an effect on another and the car has to be built as a complete package not a collection of assorted changes. As to why turning a G-body into a targa top is less feasible as a simple size / weight issue. Think about lifting both sections of the Ttops out at once from one side of the car. Nearly an impossible task for most people.
As for the rigidity of a FACTORY Ttop car they have extra bracing that a solid roof car does not. The factory Ttop cars have a structural bar built into the Bpillar and roof that adds a Structural hoop that the Tbar ties into to hold the A pillar forward. The other part is that on all modern cars (ours included) the windshields are glued it because they are designed as a structural part of the A pillar section which allows even loading of forces. As for twist in solid roof vs T roof models that is a lack of improvements by the owner/buider because in order to severly twist the frame you have to increase HP/Torque output to above vehicle engineers design. Like any modification every part has an effect on another and the car has to be built as a complete package not a collection of assorted changes. As to why turning a G-body into a targa top is less feasible as a simple size / weight issue. Think about lifting both sections of the Ttops out at once from one side of the car. Nearly an impossible task for most people.