Well, since the Sh-2 has a gross weight nearly twice your desired limit, we couldn't use it for help, much.
But I think what you're talking about is do-able. You probably remember the Two Wings Aviation Mariner; a biplane ultralight of pretty much the same configuration.
http://www.lightsportaircraftpilot.c...r/153_5394.JPG
With the additional slack given by the European limits, you could probably come up with a single-wing two-seat variant. To save design time, you could probably even adapt the wing design from a Pietenpol or Fly Baby.
I'm not sure how much overall interest there would be, but it sounds like a great personal project.
Ron Wanttaja