Hi Tom,

I'm in the process of completing a GP Skybolt myself. I also could not find any information regarding the bottom wing dihedral in the plans or instructions. I basically made sure the top wing had the correct -1 degree of incidence when attached to the center cabanes, and that the tips were positioned level to the ground and equal distanced to the vertical fin. With the top wing set this way I attached the bottom wing left and right panels to the completed interplane struts. The I-struts are a fixed length so I figure when they are properly attached to the level top wing, and the bottom wing panels are centered and seated in the saddle, it will define the dihedral required in the bottom wing. I tack glued the bottom panel halves and when I added the precut angled bottom center wing dihedral braces they seem to have the correct dihedral and the braces matched up with the spar angles nicely.
I'm not sure what the measured dihedral came out to be, but I can check later and post my results. I'm just beginning the covering stage, so I can't comment on the flying performance with this setup.
You can check out my build progress on my web page button below. Keep us posted of your build too.

Regards,
-Fitz.