Ok...I'm confused. I had just listened to a "behind the scenes" documentary on the dvd's and Lou Scheimer said it was based on a car called the "thing". I looked at the link you posted and noticed this mid-way down the page:
The van we tested, dubbed the Roamer by Automecca, was based on a '74 Thing .
I'm not too knowledgable either...just passing on what the producer of the show said.
VW 2 wheel drive vehicles of the era all had pretty much the same drivetrain. And they were stout and relitively cheap. Bugs were everywhere, Things a bit harder to come by. They could have used a Thing, but kind of wasteful when bugs were so much cheaper.