What I'm planning to do is take and reinstall the two cross-member bolt tubes in location "B" and take a piece of 1/4 inch thick steel and weld it into place like shown in this picture.
I'll then follow it up with another piece (maybe thinner like 3/16) on the topside of the floorpan.
For good measure, it looks like there is enough room under the car (near the B locations) where I can weld in a vertical ridge along the sides where the cross-member is cut out to make it even more rigid.
I'm going to make a cardboard template of the transmission tunnel tonight and start bending the steel in my 12 ton shop press.
