I take issue with this. If the side structure/perimeter is properly built/configured, including stiff bulkheads, it will more efficiently carry torsional load than a center tunnel since they are further from the neutral axis. They also have the virtue of providing side crash protection. I might also look at a diagonal between the two rear stays. Your comment on shear panels is right, but in order to really provide shear strength, they have to be rigidly fastened to the structure. Just using pop rivets won't provide enough integrity. In this case, triangulation is a belt and suspenders approach to it, at the cost of some weight. Since this car leaves so much on the table from lack of aero/downforce etc, a little extra weight is a drop in the bucket.The perimeter triangulation does nothing for torsional stiffness. Looks heavy. I would design a center tunnel running the length between the seats, the larger the better, and use sheer panels where needed instead of all the triangulation. At the rear I suspect the engine/tranny is going to be a stressed member? The rearward weight transfer on acceleration goes into the rear suspension, with the top of the shocks at that height, the only weight that transfers down onto the suspension is the weight above the top of the shock mount, not much. All weight below that point is transferred to the rear and 'locks' the suspension, does nothing for weight transfer. Course I'm not an engineer and this is worth about as much as you paid. Good luck.