A frame? Are you talking about the underside rails that appear to be a frame? Actually, the car is a unibody structure, where almost everything is welded together. The unibody structure of a convertible is beefed up relative to a coupe/fastback, and it is generally not recommended to swap unibodies, due to expense, welding, etc. Much better to start with a better 'vert unibody and transfer your stuff over.