After reading a lot of stuff on the list I've made up my list for this
eventuality -- my '85 Westy has only 47K on it.

1.  Rebuild the existing engine if physically possible -- it belongs there
and will fit better than anything else (all the wiring and hoses match up)
except a replacement 1.9L -- or a 1.9L with a 2.1L crank.  Rebuilding also
gives you a chance to add all the bells and whistles to make it better,
stronger, faster, etc..  If your engine is too far gone you could get a
rebuilt long block from a reputable vendor -- I'm sure the list can provide
much advice on vendors.

2.  Replace with a 2.0L Golf engine -- this seems to be an almost no-brainer.
 Almost all the parts necessary to pull this off are VW factory stuff.

3.  Replace with a 5 cylinder Audi/Quantum engine -- not quite the no-brainer
of the 4, but seems to be fairly easy.  I'm a little concerned with the age
of the 5 -- my Dad had an Audi 5000 many moons ago that turned into a dog
(not sure if it was the car or his maintainance habits).

4.  If you feel a need for speed and have a bunch of bucks to play with try a
VR6 conversion.  The only web sites I've seen on this are in German so I
don't have any idea how complex this is but you have to raise the deck lid.
Other than that the pictures look like it fits real well.  You're guaranteed
to have the fastest shoe-box on the block.

Chuck
Roland -- '85 Westy