I've got a 46 Merc steering box here... The shaft is about 4" longer... I can't imagine Henry going to the trouble to produce different steering gear parts for the Merc when the Ford was right there... Wonder why you're concerned, I would investigate furthur.
Karl
The box is the same, same '37-48, shafts and tubes in many different lengths overall and lengths to lock hardware. '28-48 parts book sorts out all the Ford variants, but then Merc has its own parts book.