I’m surprised to read this. This is a basic thing most know already. Have you worked on any small blocks at all? Big blocks?
I think you need to read a few books. We can’t teach you a step by step of you don’t know the basics to these engines. A “How to rebuild” book should be a must have book n your library.
There are two plugged water ports in the block on each side of the engine. I suggest you pull these out as to drain the water from the heads down to empty the heads best. Emptying the radiator doesn’t get to the heads and such fully. Even tilting the engine helps. The intake also holds some coolent. Tilting the engine a slight bit (via a jack) helps get it all. After all, the less coolant in the oil pan the better.