It's difficult to tell from the photos as they are so close that it don't present a clear view? From what I can tell(?) a new box would be best and a faster fix. Clean up the firewall when the remains of the old box are removed and perhaps cut a thin ply to cover it
and exoxy it firmly(clamp) then install the new box. I recently aquired what had heen a nice 20 cc size plane at a swap-meet with thoughts of cleaning it up and flying it. It had been repaired by the "slather on more epoxy and glue method" so poorly that I removed the servos
and other salvage and junked it.
Take a little time and it should work out!

Good luck!