The shear webs should be easy enough to remove, although to be honest it wouldn't hurt to leave them in there and just get a bit more balsa to cut extras for the other wing. If I remember, the dowel plate is epoxied into the wing, so rather than remove the one you installed on the main spars I'd get some matching ply and cut new ones to install on the front spars. The extra weight really won't matter all that much, and since you're installing servos in the wings the plate in between the main spars isn't going to get in the way.

Cheers,
Neil.

As my old driving instructor used to say "Experience doesn't stop you making mistakes... it just lets you cover them up more effectively!"