Brakes for the Missile-need advice

I have ordered a tubular front end from Denny which uses Mustang II spindles. The question here is whether I need 12" discs or will 11" do.
The 11" solution is easy and relatively inexpensive, the 12" route is more complicated. I can only find 12" "Drag" brakes from wilwood, but they are .81" brakes and look substantial.
Im up for tech advice here.
Thanks for your help
Andrew