I had the same problem - got an F180L (name Optimus G is the same as on the real E975)...
My problem was/is that FreeGee bricked the phone totally! Only download mode still working... I was coming from rooted stock Korean ROM 4.1.2. (F180L20S or F180L20R)
With the download mode I flashed TeenyBin and pushed via ADB a custom rom (CM10.2 that time) and GApps,
voila - CM10.2 installed.
Do not use TWRP as it has a different model identifier and you would have to modify CM ROM everytime you flash them, stick to CWM 22.214.171.124!
Also - do not flash any different BASEBANDs - as it is korean, you cannot change the available frequencies with simply flashing a different!
In germany I could live quite good with the korean one - LTE was no option for me (which would never work in germany though with a F180L)
But 3G and 3.6G+ (HSPA) was working well! (2 different networks tested: Vodafone and O2)
Hope thats helps a bit
But my next step is: revert back to stock as described in this thread:
As I got my Nexus 5 and want to sell my good "old" F180L ;)