As for what to do, it's usually easier to cut one wing shorter, than extend the other.

You can cut through the spars and skin sections just outboard of the root rib, at your 1/2" dimension, then grind and cut the remains from the root rib, or fabricate a fresh one.

The new root rib should then be inserted and epoxied into the prepared open end of the wing. Same for your aileron.