Whilst doing the rounds on Alibaba, as you do. I came across the hercules dv210 diesel v-twin. It's weight for what it's worth is quoted at 85kg. And having had a quick chat with the merchant, apparently they are working on a 60 kilowatt version of the engine. All in all I believe that this engine could potentially fit in the Rotax 912 UL niche, at about 190lbs and 80hp. Potentially encouraging for those interested in burning diesel or Jet a.