Use 8 oz. C40 and 4 oz. C60. Nix the rest for this beer. It will be toooooo sweet.
Add 3 or 4 lbs. extract early, and the rest at 15 minutes left in the boil for better hop utilization. Do a full volume boil with no top off water if you can. (You should be able to by avoiding displacement of water by adding half the extract late).
Cut the Columbus to 1/2 oz. at 60. Move the 20 minute addition to 10 minutes and double it. Double up on the flameout addition also. Lastly, add a 1.5 to 2.0 oz. dryhops during the last 7 days in the primary.