Some of you may remember reading about my 1982 300D that I installed a 4.3 liter Astrovan V6 in - I have driven it for about 8 months now, and have taken several longer trips with the car, so I can now report that with 4 people in the car it will produce around 28.5 mpg, cruising at 80 - 85 mph with the A/C on. It gets around 21.1 mpg in average around town, go to work driving. I think this is fairly comparable to a diesel engine in the same body, so I'm very satisfied with it, since it has much more power than the diesel did, and the engine rpms are a lot lower so the engine is very quiet. (around 1650 rpm at 60 mph, 2960 at 100 mph.)
If you are interested in reading about the conversion you can view my report at: http://pages.prodigy.net/rwooldridge/mercedes.htm
One bit of information not included yet is that you can get the right pan for the conversion from an engine in a 4wd S10 or Blazer. Turns out that they use a pan that's pretty much identical in appearance to the mod I performed on my pan.
'82 300D/4.3 L V6
'85 GMC S15