Indeed, I am looking for a broken upper receiver. The part I am interested in is the rear section, so if you have an upper receiver that is no longer servicable, unsafe to use, flat out cracked, split, broken, etc. it is fine by me - as long as the the tail end is still intact, including the rear take down pin section.
If you have such a piece, please let me know. I would prefer a picture to confirm it will work for my project.
EMAIL me at TEPPOJUTSU(AT)PEOPLEPC(DOT)COM