The 16v VW engines are not known to have a lot of torque but rather develop
their power high in the rev range.  In other words you have to make the
engines sing before you get the extra benefit of their advanced design.
For a Vanagon I would have thought that engines that develop healthy torque
at low RPM would be more suitable.
Having said that I dont know which among the VW engines would best meet that
description.  Probably the Audi 5 cyl.
A good engine to use would be the 2.7 litre 6 "eta" from BMW which is known
for high torque and high economy.    Whether it could be made to fit of not I
confess to not know.  I just have a fondness for the grunt it puts out .
Just my tuppence worth.
Steve