Highly experimental; Wi-Fi and Bluetooth may work, but SIM/calls and GPS are often broken. CyanogenMod (Android 6.0.1)
The device's hardware profile dictates the feasibility of custom ROM work: Qualcomm Snapdragon S4 (MSM8227). nokia lumia 520 custom rom work
The dual-core processor and low RAM make modern apps nearly unusable on any OS version. Highly experimental; Wi-Fi and Bluetooth may work, but
The original for your specific model (found via LumiaFirmware). Step 1: Unlock the Bootloader Wi-Fi and Bluetooth may work