If you were carefull it can be done. I would use a thin diamond blade in my dremel and make the cuts down the side where the rails were to be glued in and then remove that balsa. Now make the mods needed to the bay as necc to install your gear and some good hardwood blocks. What I did on this one was remove the existing ribs on each side down to the ply floor but no lower leaving the ply floor which is actually not the floor since the wing is upside down at this point. Now make the hardwood blocks for the rails. Now that these are made make some new ply ribs but make sure that they fit good with good contact all around these will be glued in beside the rails. Now before I glued anything in I made sure of a good dry fit after that I glued in 3/8" and 1/2" triangle stock anywhere I could to beef up the area. Now I glue in the ply ribs making sure of plenty of 30 minute epoxy especially at the front and rear of the rib where it attaches to the spar. After that is setup I glue in the hardwood rails making sure that all areas that contact wood have 30 minute epoxy on it. Now if the blocks are very true then since the ply floor is still in you can use that to glue to and it should be square to the wing so that the gear should be sitting at the correct angle. If you do all this carefully all you should have exposed is a bit of ply on each side about 1/8" that you can take a brush and touch up. Just use your imagination and your preveous experiance it isn't that hard and it will be much stronger in the end. Oh and have paper towels ready already torn so that if you get glue on the wing you can get it wiped up right away. Hope this helps hard to explain perfectly.

Randy