Or, if you could post up some more pictures of the van from different angles, inside and outside,
it might "ring a bell" with someone. I'm guessing that if it was a P/W there would be some sort of
P/W badging on it somewhere, door frame edge or somewhere inside or elsewhere on the body or
frame, or inside/under the appliances.
A really long shot might be to see if you can get the VIN number, or the engine ID number(s), and
see if Dodge/Chrysler have a record of who it was originally sold to, prior to being converted.
Like I said, it would be a long shot, but you never know.
Same idea, If there were an unusual appliance or a custom part or fitting with a serial number,
you might be able to trace that back to the appliance/part manufacturer, and then see who it was
Again, long shot.
This link has some information on Dodge vans over the years and might give you some clues.
There's even mention of "conversion vans" in the blog, and some were factory built (it's a long
blog, but there are pictures and some interesting historical commentary).
About halfway through the blog there's a picture of an ambulance with "Photo C" embedded in it,
and the van model in the pic, looks like your van.