if you listen to the recent can-you-brew it episodes on arrogant bastard, it's 90% 2-row and 10% special-B. they're pretty certain that there are no other specialty grains. the hop schedule is 1oz additions of chinook at 90,45,15 and 0 minutes.
also the yeast is "dry english ale" yeast, wlp007.
so I'd make those hop and yeast changes, plus I'd use 8lbs of light DME and 1 lbs 9oz of special B for steeping.
I would probably wait to add half of the dme until the last 15 minutes in your situation. though with the over the top ibus in this beer I don't think the reduced utilization will really be all that perceptible.
your recipe will undoubtedly make good beer, though.