This sounds nitpicky, but if you're using 10 pounds of MO, you're not making an ordinary bitter. For a bitter, your OG should be 1.040 or so or under. With 10 pounds of MO, you're making an ESB.
So, if you have an OG of 1.054 (75% efficiency) you could do 2 ounces of fuggles at 60 minutes, and 1 ounce at 15 minutes. That would give you 33 IBUs, barely enough to balance the malt but still within the guidelines of an ESB, and a IBU/SG ratio of .6. Your color will be very light without any crystal, but it'll be a good beer.