I'm not sure if the weihgt is similar, but Hummel also makes a 1/2 VW
engine but in all of their planes it puts it over US ultralight
weights. IIRC (and I might not), the difference between the equivalent
2-stroke Rotax was around 25 pounds. If you start out with a light
enough design to begin with it might make it.

One major plus with the 1/2 VW is the fuel consumption. From what I've
heard it's down around 1.3GPH. That's some pretty cheap flying .