I disagree, Cent and Cascade are highly compatible / complementing flavors. They'd work just fine!
You're in Texas, and you said you ain't brewing this immediately........ What about picking up a couple of oz of Riwaka from Austin Homebrew? It's described as "Riwaka's powerful grapefruit citrus characteristics are breathtaking." and "This hop is an excellent substitute for the West Coast "C" hops. Think Centennial, but not as harsh." (And their hops are on sale, today only, in case you didn't see the post!)
That could really be the way to tie the rest of this together.
But I LOVE your hopping schedule, and think your grain bill is teh tits. Love it love it love it.