Add the following URL to the Arduino Boards Manager (File->Preferences).
https://github.com/watterott/ATmega328PB-Testing/raw/master/package_m328pb_index.json
Update the Arduino AVR Boards to version 1.6.22 or higher via the Boards Manager (Tools->Boards->Boards Manager).
Install the ATmega328PB Boards via the Boards Manager (Tools->Boards->Boards Manager).
The output compare will only work if a 1 or 0 is written to the port register depending on the modulation. Futher infos here: http://www.avrfreaks.net/comment/1717946#comment-1717946 and https://github.com/watterott/ATmega328PB-Testing/issues/29
ATmega328P and ATmega328PB have different thresholds for reset. This can be a problem when using a 5V power supply for the microcontroller and an USB serial adapter with 3.3V logic level on DTR.
The ATmega328PB has no full-swing option for the oscillator.