By no means am I a source expert on frame boxing or monster motors, but I can tell you my experience so far. Before, I tore my car apart I noticed that when I used a floor jack to lift the car up under the frame the doors would not open on my 67. I was putting jack under the first body mount area, where the frame starts to curve toward the engine bay. I have now boxed the frame completely and can put the floor jack in the same spot and the door will open and close fine. My body mounts were also completely dry rotted before I boxed the frame along some other rust issues that could have also played a factor in the car flexing. I am a firm believer that the entire car as a whole is more solid now, but if its necessary I cannot answer. I had my car off the frame, so I figured why not.