is there a consensus view on the wing brace/jig/gap...
Without the wing in front of me, and please accept my apologies in advance for anything that is blindingly obvious, my suggestion is...
0. Measure the current tip dihedral.
1. Cut away the tissue on the underside of the root panels on each wing. Leave a flap of about 1/2", errr 13mm, on the tissue that's left in place so that you can glue the cut edge down and get enough purchase on it to keep it taut.
2. Cut the brace at the mid point to separate the wings.
3. Carefully remove the bits of brace from each half.
If you haven't got a v. fine scalpel saw. Sand down the brace where it lies along the spar until all gone. Cut it as flush to the outside of the rib as possible, then san flush. Use a fine drill bit in a pin chuck, or your fingers, to drill out most of the brace where it goes through the rib then using a cut down emery board sand out the slot. If the root ribs suffer a bit splint them on the inside with some scrap sheet. Won't make a significant difference to the AUW.
4. Cut a new brace. I would use 1/16" ply but it's not mandatory.
If you are using balsa use the hardest you have to hand. Nick some scrap from the Bird Dog kit if needs be.
5. Re-assemble wing with root ribs glued together making sure you get the tip dihedral close to what it was. Don't worry if it is not exactly the same. As long as it's symmetrical and not wildly out it'll be OK.
Clamping the root ribs together while the glue sets might be a bit tricky with the top root bay panels still covered. You could prop the wing up on blocks to give clearance underneath for clothes pegs/clamps or use fine (silk or dress-makers) pins through the top covering to hold them together. Do a dry run first to see what works best. If push comes to shove cut the tissue away from the topside root panels.
6. Re-cover the underside panels.
7. Sit back and enjoy the glow of a successful repair and the re-issue of its CoA.
Andy or JonBuoy might have better thoughts.
Cheers,
Lurk