What I have found while deciding on the same subject,
   First of all there is no oil temp sending unit that will fit or screw
right in.  The VDO sender will not fit in the oil plug hole and therefore if
you want oil temp you must drill and tap a hole in the case.  Oil dipstick
sending units are not recommeded.
   For oil temp you need to install a sending unit as well which will take
some time.  Visit the main Vanagon page for more info and articles on this
procedure.  Go under problems and then the low oil pressure light for the
leads to it.
   What I did with my sender unit.  Alot of people mention many differnt ways
to mount  and run the hose, showing concern for bends and heat.  I brought my
hose up the back of engine (towards front of van) and under thermostat
housing. (I have a 2.1L)  I tapped the hole on top of the driver side
cylinder head and mounted the strap there along with its own ground wire.  It
does have a bend in it but it is away from the heat of exhaust pipe, I do not
anticipate any problems from it being bent.  And since it sits on top of
engine it is accessable and stays pretty clean.
  As far as mounting.  I have not mounted my gauges yet, but plan on doing it
soon.  My first choice was to mount them on top of the dash between the two
defrost vents.  There is a little lip there that the holder would fit nice.
The only problem is it will overhang a little bit, off the lip towards the
window itself.  I am not sure but I think the dash boards are a bit differnt
possible changing in 85 or 86, and I think this lip is a little differnt.  I
have also seen pics of installations where they were mounted in the dash to
the left of the cig. lighter.  This was a clean install, but you can not see
them very well and you will need to cut holes in your dash, with a hole saw.
  I believe I will probably go with the cluster on top of the dash, I have
been trying to find some differnt models with not much luck, to see if any of
them would fit better that others.  Will probably just go with the VDO one
that BD offers.