Well, IMHO, the servo arm shown on the plans is too long. If you use that you will still have to dial down the throws too much. Either move in on the arm or install a longer control horn into the elevator.

BTW, the 9411 is a great servo. It is smaller then an 8411. I'm not sure if it will fit in the stab, but it is a bit narrower then the 8411. A pair of those on the elevators should work fine.