This v4a is working on A12... Install the apk and Just toggle legacy mode and compatibility mode until you start to hear a difference
https://www.dropbox.com/s/b0th2nvkbcu9nre/viper 4 android.apk?dl=0
And make sure you back everything up, formatting data wiped my internal storage and files
Pardon my ignorance. I'm familiar with GAPS but not Viper? What exactly is Viper? Is it an alternative to GAPS, or something that runs with GAPS?