Why doesn't my billet front drum fit?

So I bought the hot-****, half-a-mortgage-payment, billet front drum from TCS. http://www.tcsproducts.com/products/product/tf727-steel-front-drum-aluminum-piston/

Now my transmission won't go back together cause the pump body is bottoming out on the drum, even without any thrust washers at all. It goes together fine with the old cast iron drum, but that sort of defeats the whole purpose.

I feel like maybe the product page shouldn't categorically recommend it "for street & strip" if it doesn't even fit in the goddam thing. There's not even an asterisk with "this doesn't fit yours" info.

Just wondering what multi-hundred-dollar machinist work of art I have to buy now to make it work?

C