Do I need frame connectors?

My 68 Barracuda is starting to show a small crack at the end of the rocker panel right at the bottom corner of the drivers door. Is this an indication of the frame twisting? The car is equipped with a 440-6 and a 4spd. with 3.91 gears. In addition the passenger door used to stick some but doesn`t any more. Do I need frame connectors? Has anyone else experienced this? Thanks