With the bigger motor and extreme power that you're using I'd go with nothing less than aircraft ply rather than lite ply for the wing bolt receiver plate and at least two hold down bolts. Plus ensure it is firmly glued on at least three sides. Based on the picture it looks like the receiver plate wasn't firmly glued into in the fuse on three sides as it failed in the middle. I still don't see a lot of time consuming repair though.
Joe.