Below is an e-mail I got from Steve Sandlin --- the VW Lock Guru about swapping
the door lock cylinders.
Still haven't done it myself. He'd definitely be the man to ask for further
details.

Cheers,
Doug
'84 Westy
Toronto, Canada

Remove handle.  Small recessed flat head screw in hole that is generally
dirt filled.  Remove screw.  Slip plug outpossibly pushing out from front.
There is a small spring on end.  If you look at the plug, You'll see marks
in the casting where it rested before.  With spring in place, put in new
handle.  Tighten screw, but not so thight that it binds rotation of lock in
handle.