Engine block drain plug and pet cock install

[mike16]

What size Allen wrench fits these drain plugs in the side of my 72 307?

I want to install pet cock style drain valves in this location.

What size threads or a part number for the correct drain valve?

Any advice on removing these plugs while the engines in the truck.

Thanks all!!

[Shifty One]

IIRC, they take a 1/4" hex. As far as pulling them, I'd soak them with your favorite sauce for a while before assaulting them. I like to rap on them a bit with a plastic-faced hammer if they give you problems. Might want to have a small butane torch available on call, just in case.

[leegreen]

The thread is 1/4 NPT so that should be 1/4 hex socket.
Use a good quality tool, it may be very tight. Breaker bar tight, the thread size is close to 1/2" bolt