Navy,
I went back through my build thread and found this picture of my center cross member, which is similar to yours, done by the guys at N&N. Note that they boxed the center on top, added a tranny mount up front across the bottom with a removable center section, and then added a bottom brace in back that acts to hold up the driveshaft if the front u-joint happens to blow. I think most commercial frames have similar cross bracing.