I'd been looking at that blue bit as well! I thought it could be a central (swept?) fin since the original beast seems to have been a bit unstable in yaw. However as you point out, it also appears possibly to have the wing tip fins and I cannot find any evidence of one with all three.
My bet is that it is one of the plan-built early Backstroms with some local modifications. This was the start point for the more refined (I've just noticed , also with apparent dihedral) Marske family of "Planks" in any event, so we're all in the ball park.
Last edited by RETDPI; 3rd Dec 2007 at 12:39.