I checked my Kombi, which is an '86 and so has the 2.1 liter engine.
I never had looked before, but it indeed has a single groove pulley.
I looks a lot like the old pulleys on the Type1 engine.

The Kombi is the only waterboxer I've seen without any options (except
the Syncro option) -- no power steering, no A/C.  No opening windows...
In any event, VW certainly made the single groove pulley, and installed
them on real buses.  At least by a sample of one (but then there are not
all that many plain-Jane Kombis in the late line, either, one is a large
fraction).

malcolm