Nothing in particular, it could be used, but I'd rather having matching sexy billet pieces than mismatched. Materials cost should be minimal for these in 6061, its the machine time that's going to cost. I may end up adding a cover to hide the gauge bracket to the top piece.
Also, the stock pieces are not light.
Looking at them together, I have a strong feeling the Scotts' going to be too wide to fit like this.