Don't think that you need to build a new wing. Pretty sure that the wing can be split at the root. A couple of (or one) new root shim can be made to eliminate some or all of the dihedral. Use a chunk of decent balsa block and sand it to the outline of the original root ribs. You might consider cutting the covering back away from the split so that you can run a 1" strip of fiberglass over the finished seam. Some use thin CA to lay down glass and others will use either Finishing Resin or 30-min epoxy diluted with alcohol (epoxy only - resin is thin enough). Don't go overboard with resin or epoxy 'cause it's a real B to sand. Fill the weave with filler. Recover making sure that ya got 1/4" overlap.

As far as clipping a rib "bay", covering is cheap - use a hot iron and seal the existing covering to the "new" tip rib and then run a sharp razor (aka - new blade) down the outside of the same tip rib. That will leave a flat wing tip. Cover it asis or fab up something you prefer. If you think that it's too soft lay down a new tip rib using 1/8" balsa and sand to shape. Then cover it overlapping the existing (sealed edge) covering making sure that you have 1/4" of overlap.

Hey - it's all practice ... 'cause we never get it just right.