Freezing temperatures - water in engine

Funny you ask this question. I drained the radiator on a friend's 69 dart 360 (at my house) when I knew the temps were going to drop low. Next morning....(and I got this feeling of horror around 2am @ the residual water in the block)......I rushed out to find a freeze plug laying under the car.

Sure, I was thankful that the block hadn't cracked, but of course it had to be the freeze plug right behind the steering box.