I'd probably drop the chocolate and crystal 80 to .5 pounds (maybe .75 for the crystal). You might also consider adding 2-4 ounces of cocoa powder near the end of the boil to add actual chocolate, perhaps bumping the crystal to .75 if you do this (since cocoa is bitter).
EDIT: You may also want to look at Northern Brewer's Chocolate Milk Stout recipe for ideas (minus the lactose).
EDIT2: I wouldn't do the Chocolate Milk Stout without the lactose. You'd need to add more crystal if you dropped the lactose.