The Volkswagen Wasserboxer
Lots of links to illustrate.
It was A type 4 VW Engine with water cooling bolted on, with a
weird "rubber lip" headgasket.
see
http://www.gowesty.com/library_article.php?id=107
and
http://en.wikipedia.org/wiki/Wasserboxer
I hade a 1.9l specimen in the Van pictured here:
http://www.flickr.com/photos/ppc/sets/72157594157040210/
And, as a bonus of sorts, it was controlled by the Awful-Awful-Awful VW "Digijet" Fuel Injection system. It would not run right, ever, it had this condition where the idle would go up and down constantly. The engine would bog down and refuse to push the van anywhere unless I ran with the O2 sensor unplugged. Google "Vanagon syndrome".
The later vans had "Digifant" which was moderately less awful, and was supposedly a system used by other late 80s VWs, so at least parts can be found for that.
Also, see the '71 Microbus my father had that got *squished* by a HEUG Oak tree in our front yard.
http://www.flickr.com/photos/ppc/253634236/
Forgive my many links, but you can read about the 5 (!) rear engined volkswagens my family had here, on my forum.
Page has lotsa cursin' in it though, so don't click if easily offended, or at work. The reason for this, as you'll see, is that the VWs were not fun to own.
http://www.network54.com/Forum/405166/message/1164541826/