Looks nice, far more elaborate than what I was thinking of doing. I like your idea as it looks like there is little chance of it moving, but then again it looks like that could create the stiffness you don't want. Testing will be the key.
You can't have much left of that broken chassis now, lol.
For the split block, I wonder if the Tamiya ones could be adapted to the car, Ed probably has the center on center measurements for both cars and would know if the pillow ball would fit as well. Or perhaps use both Tamiya pieces at that end, as I'm sure they both use the 3mm pins.