Frame Rail inside dimension needed

[bigmau]

I have a frame rail that is buckling due to the bottom being rotted out. I think rust is cool and all, but after driving it for 15 years I've made up my mind that it is time. Can someone provide me a dimension or measurement for the distance between the box plates inside of the frame rails? I have a Gerson order on the way, and I suppose it the same dimension as the front crossmember width, but I'd just like measurement for reference. My plan is to fabricate patch pieces, jack the rails apart until they are true and my body gaps are good, and then rebuild the rotted out lower sections. Any help would be greatly appreciated. Thx.