Replacing Head Core Plug

Hi,

The core plug in the back of my passenger side cylinder head has popped out. It was one of those rubber plugs that you can expand with a wrench. I would like to replace it with the proper brass plug.

The engine is a 1974 Dart sport 360. I am struggling to find the correct plug size. Does anyone know the rear plug size for this head? Also any ideas how I can press that plug in without removing the engine or head?

Thanks