just a quick thought to help with the "chassis bending".
i wonder if mugen could use a system of a "tube inside of a tube" as a rear side stiffener. Imagine two steel, or alloy tubes, one fitting inside the other. both tubes have each end sealed off. these two tubes would go where a normal front to rear brace on a convetional tourer design would go. being tubes, they still allow the car to twist from left two right, but being sealed tubes they provide strength when the servos apply braking force.
here's a picture of the idea. it seems like a simple enough idea, which does not eliminate the mid chassis flex, whilst at the same time providing the much needed support on the rear of the chassis to minimise chassis bend and improve brake pad bite and performance.
the tubes don't necessarily need to be cylindircal, it's only the internal tube that needs to be cylindircal, but this one can be solid for more strength. the external tube can be cylindircal on the inside and a square shaped outside for greater strength, or orientated as a "diamond shape" to position the strongest points (the edges) at the areas receiving maxmum force/leverage., to bend something like this would require similar, if not more force than conventional plastic or alloy braces on conventional tourer designs.
i've attached a picture, hopefully it explains the idea better