Whoops

While taking my car out for a local short little drive I blew out a cylinder head freezeplug. Whoops. I'm guessing that between old freezeplug and not having the thermostat opening just yet when I checked the condition of the floor under the go pedal caused the pressure spike and popped it. Anyone know offhand what size the freezeplug size is on the end of a smallblock cylinder head? Luckily it's the drivers side front and very easy to get to. Being that this is a dropped in motor with nothing done to it I'll just use a rubber expansion plug type.