Clean, rough and clamped are the secrets. If you know anyone with a sand blaster and aluminum oxide that should do well. As for cleaning, brake cleaner or Lye (draino powder) in water and then rinse. If you really want to do it right wear latex gloves. Hope you get it.
J.B. has fixed a lot of unfixables for me in the past. Engine blocks, stripped weed-eater head threads, etc. I've always used clear epoxies for gun stuff. Tried 5 minute stuff last time on a gunstock, it set after the wood shifted, I ended up sanding away alot of wood.