I would love to hear Len's response to this. Based on what I know, I would say that this is impossible. The key measurements are the backneck, and the length of the shoulder seam. You can let out the backseam all you want (provided there is cloth in there) but that will not change these other two measurements. It will just make the back of the coat more roomy. The fundamental problems: There is no excess cloth at end of the shoulder, at the sleevehead; you can't move the armhole; you'd have to take the coat apart and put in a whole new pad and superstructure. Even if it could be done, this is a classic no-go alteration. Find a better fitting suit.