Is a gearbox for engine number ADY interchangeable with gearbox for engine number ADZ?

You'd have to do some measuring...if you have good 3D perception skills could instantly see if this will fit, not sure about a tranverse configuration, kinda touchy, quite surprised that they were able to fit 1.6 and CVT in the small engine cavity of the MINI, so VW isn't going to be much different, no doubt they wasted NO space, not even wrench room, I remember losing a 10 mm socket while working on a GOLF...seemed fussy and uncomfortable, compared to an Oldsmobile or Buick...you'll have to be careful with clearances and shaft length, control linkages and plumbing.

Yes it will fit, it is the same gearbox the only thing that changes is the gear ratio. So the car can handle differently when you change the tranny but not a big deal.