I am doing this very thing.  In the rear of the normal Vanagons after '82
there are attacment holes for the diesel motor mounts (the diesel Vanagon was
still being made in Europe).  So it should not be hard to put a inline gas
engine into a newer Vanagon with the wasser setup using a donor diesel van.
The hard one to do is to put a diesel in a wasserboxer Vgon.  Something to do
with the fuel tank setup being different?
Thats all I know.
Ken Wilford
John 3:16