Hi Don, I can't find the original drawings of the ply gussets but this is basically what I used (adapted to dowels). They are interlocking (sort of) and connect all surfaces of the joint. I actually don't think this would be necessary for a very light model considering how fiddly it is to make them, a more basic gusset in plane with the formers would probably suffice. You could make it from slighly thicker material to give the cross beams a surface to adhere to.

That's really a very elaborate experiment of yours! will that morph into a model at some stage??

It's a pleasure to drop by and observe your work!

BTw, i am still intent on building a DIII, like the eindecker the original had tubular construction so I'll be following this thread with great interest.