Kirk's point on the rear towers is well taken, but the solution is to bend a plate and tie the plates together such as they constitute a "single" mounting plate within the 144 square inch rules for all tubes on the tower.

You would cut out those diagonals going from the Main hoop to the center hump on the floor and relace them with a single bar spanning the main hoop--level side to side.

I hope the sill bars are not stitched to the rockers along their length. If they are not, you can fab a box in the floor-B-Pillar area where the tubes join (on each side), and the box when welded in and to the tubes will be your mounting point. If they are stitched, you will have to break the stitches.

A bit of work, but that is a stout looking cage.