Its sounds like the air-cooled Vanagons have several things in common,
judging from this discussion, as mine also suffers from  the same
maladies as yours:

Head temp: the VDO gauge I have reads 350 at the mid point and goes up
to 600. I have been told that 600 has been seen in some hot rodded VW
engines so i would think 350 is around the norm. As for the readings
on th 82 westy, this depends. Initially the head temp sender was installed at the same
point as the FI head temp sensor. In that position the head temp never read
above 250 well past the median mark on the left. Then I moved  the head
temp gauge sender to no. 3 spark plug and get readings between 300 and
350 (350 at highway speed). Judging from what others are saying the
latter reading is more accurate and well within the normal range.

Oil Pressure - I too had a similar problem with low oil pressure at
speed. When we drove down to San Diego and back in mid-seventies
temps, the oil pressure would not exceed 20psi after having been
warmed up. Eventually after driving up hills (Yosemite) the oil light
would come on. At that point I decide to put in the second cooler and
now the oil light never comes on at idle and psi is up a fill 10-20
psi at speed. Granted there could be a fault with the gauge but this
is unlikely since the gauge reads 7psi, exactly at the point where the oil
light should come on and it does.

Apparently as you say there should be a minimum of 28 psi at 2000 rpms
(Haynes) or 42 psi at 4500 rpm. My feeling is that if you aren't
getting at least 10 psi per rev. then something may be wrong. The
problem is in the design of the cooler (judging from David S'.
description of it - it should be bigger with more cooling...capacity).

Oil temp - I have no oil temp gauge yet but assume that it is in
operating temps..... with 20W50.

DC