How To: Fold down seat conversion

I just purchased a "shell" of a 67 Dart GT that has been poorly tubbed with a four point bar installed. I have considered removing the bar and re-doing the tubs to improve its intended finished curb apeal. The cross bracing has been removed, and I can't find it anywhere on-line to restore body rigidity. Intended use is 95% street, 5% track. 440 X 727 X narrowed 8.75 with 4:10's. Any recomendations about how to replace that cross bracing or otherwise restore body stregnth?