It would not hurt atall.Actually 4 inches is pretty close .The section for an omc was 5 inches to make a long shaft.If you go the new transom route you have the opportunity to make shure the motor is perfectly centered also.
If it's a long shaft could redo/raise the transom to match that size OB, adding a jack plate will offset OB's weight aft which is not good for such a short boat. How about posting pics for visual clarification..
