I have put propane fumigation systems on turbodiesel jettas.  A fair bit of
work but it worked good.
In the quest to get more power out of a diesel, I'd turn up the fueling
first.  That only takes 3 minutes of your time.

I'm not sure the VW diesel block and head can stand much more output when
used in the heavy vanagon.  The oil temp in my TD westy
would go through the roof on long hills. Exhaust gas temp would get too high
as well.  Water temp would be normal.
I would suggest to anybody who has modified their turbo diesel to get a
pyrometer for the exhaust.  On hills, I would basically drive only as fast
as the pyrometer
told me I could.

Intercooling worked as expected, for every degree you lowered the charge
temp, the EGT would be lowered by the same amount.

Propane powered vanagon
http://www.telusplanet.net/public/gary2a/rack/propane/propane.htm

Gary Lee