I honestly don't believe the 6.6 chassis has more flex than a 6.0. Especially one that has been modified for sideways battery. This thing is thicker and heavier and more rigid.
I feel like reducing chassis flex is their goal because the only use for the block on the battery strap as far as I can tell is to limit chassis flex.
Now I really don't want to mill this lightweight chassis because it is so thin I'm afraid it will fold into a taco...