1.9tdi FTW!
If you want a 1.6 non turbo diesel VW in a truck just buy one; they are cheap. Very slow, but cheap and efficient. Edit:
http://www.mpgomatic.com/45_MPG_Pickup_Truck.html
I've got a few friends who have owned them in the past if you have any questions.
There is a thread on TDI club about putting a 1.9 in a toyota Pickup; looks like a nice swap. Edit:
http://forums.tdiclub.com/showthread.php?t=176999
Edit: I'd recommend that you stick with an automotive diesel, most of the industrial / equipment units run fixed injection timing which is less than ideal for street use.