I've rebuilt much worse!
Well worth rebuilding especially at the prices that Moss Box cars are fetching....and to think there was a time when folk used to discard the Moss box in favour of a Rover 4 or 5 speed unit!
Andy G/MOG615 is quite correct when he says that the late Plus 4's have the HR prefix Moss gearboxes. My 1968 Plus 4 has a HR prefix
box
Arwyn