The original question was about frame connectors for an early (1966) "A" body. I am not sure that they are commercially available. If they are, naturally they would help strengthen the chassis (almost anything would). I believe that unless there is an overwhelming need to have the floor under the seats appear stock, it is much cheaper and much stronger (especially with the '66 convertible) to slot the floor and weld everything completely solid. Just my 2 cents.