Not a convertible, and not an A body, but I had to replace a section of the torsion bar crossmember as well as the floor pan. No bracing at all, just supported from underneath. I sourced the end piece of the crossmember from an original car, gusseted the inside and laid a thicker piece behind it at the rocker. It all went together very nicely, and I haven’t had a problem since. I drilled and cleaned the original pan out and cleaned the flanges for plug welding.