If you want to do it temporarily then you can just get a generic oil pressure
gauge from your local Napa for around $15.  This comes with a manual gauge, a
short run of hose, and the fittings you need.  You will only be able to see
the oil pressure readings while the van is stationary using one of these
gauges (unless you hook it up with a long oil line running up to the front
per instructions on my website <see url below and click on my picture>).

As a PS the manual gauge hookup should only be done as a temporary thing.
When I took my heads off a few months ago I found the plastic line by the
engine had cracked due to the heat and was in failure mode.  In the future I
am thinking about setting up an electric gauge setup (ala VDO).
Hope this helps.

Thanks,
Ken Wilford
http://www.vanagain.com
John 3:16
Phone: (856)-765-1583
Shop:   (856)-327-0027
Fax:     (856)-327-2242