We need linemen more than anything to play the 3-4. We need a NG desperately, as well as at least a pair of 2-gap DE's. Carlton Powell could MAYBE play one of the DE's, he is a run stopper and has faced double teams before, he is pretty good at facing the play and uses a stacks the point of attack more than he relies on quick burst like Thomas.
If we do switch to 3-4 I expect our 1st draft pick will be BJ Raji who will go in a rotation at NG right away. I expect we will be after a smallish DT in the middle rounds, maybe one of the Georgia Tech guys.
If he is still there in the 2nd round Cushing could come into play as an OLB. He is a Calvin Pace clone.
I think Jarvis Moss will get looks at OLB, a lot of people liked him as a 3-4 OLB in the draft back then.