Mk3 rear beam in MK2 is not a direct swap. The rear end may bolt right up however the proportional valve location differs and the brake lines needs to be extended. The unit on my MK2 rear beam was extremely rusted and doubt operational. And the unit on my newly acquired (not new) mk3 rear beam is also busted.
This is a common issue that is overlooked by most owners and some choose to bypass the valve altogether in order to save a few monies. That valve adjusts the rear brake bias based on your payload on the rear beam regardless of the brake setup (I'm keeping the mk3 drums).
Not to deter anyone from this swap since it is an overall upgrade over the mk2 unit, however it requires one to drill twin bolt heads in order to replace the valve unit body. Sorry for the potato pics.
Even worse, in the event that you want to change your swing arm bushings, you'd have to drill off and replace a perfectly working unit since the bracket bolts are inserted from the inside
You know there's a saying with VW/Audi engineers... throw them a ladder in a hole and they'll fabricate a shovel to get out of it.