https://en.wikipedia.org/wiki/Isetta
You would be REALLY increasing the HP over what this had factory..but with some performance mods to suspension, and probably a bit more "frame" strength welded in...it would make a nice super mileage vehicle...if it could get 95+mpg factory standard..imagine what a uber efficienct diesel, idling along would get out of it...
I doubt you would find a factory converted pickup truck version...or the 600 model (enlarged)..but..you could probably modify any of the base models in a similar fashion if you wanted to.