1964 Chevrolet Corvette excessive heat in cockpit

I own a 1964 roadster with factory air. The car is in excellent condition and never runs hot. There has always been excessive heat inside the car after driving approximately 30 minutes. I have installed insulation on the floorboards (under the carpet) but that has not helped at all as most of the heat seems to come form the engine/manifold area? Any ideas?
Hagan Codell