So you have outside rails, right, and then a big X to stiffen the frame in torsion? Early fords had that.

Something to note is that the outer edges of the C section do most of the work, you are safe in cutting out the web or making existing holes bigger.

Some have built tubular replacements for the entire X, while others have cut out the center of the X and built a box that connects both sides. Without the center of the X, the car loses its torsional stiffness. So you have to have something...

It's a lot easier to do this and fit an exhaust system in, when the body is off the frame.

R.