If its help somehow, there are several cases similar the one that you have:
In my opinion, you have 4 different choices:
1- Try to flash SGH-I747 Stock rom with odin form Sammoblie- It supposed to work, but i don't familiar with the outcome in a case where your phone was been unblocked to use in other countries and carriers beside AT&T.
2- Try to install custom recovery following this guide:http://www.teamandroid.com/2012/08/2...sgh-i747-odin/
and then try to install custom rom (considered to be less risky than the first choice, but yet again...)
3- Try to start your phone with safe mode (just pressing vol down button while it starts up), and try to instal CPU-z for android to check your real phone specs.
4- Try to ask the same quastion in above forums, hoping that someone has figured out a way.
Sorry for not being too much of a help at this point