The WILL should be more of an athletic guy who can blitz, slice in and chase down plays from the backside, etc. He's typically a little bit smaller than the MIKE. I'm thinking 6'1" and 225-230 lbs. would be pretty ideal. The MIKE is a bigger guy and has to take on more blockers, so you'd want him to be pretty stout; I think Kenny Demens had a pretty ideal frame (6'1", 245-ish), but he wasn't as instinctive as you would want.
that is nice bonus change