Foundry workers automotive science lesson for the day
There is no such thing as a "freeze " plug in your engine block. those holes are there so that the sand core that the block is poured around, can be shaken out after casting. You are just as likely to crack a block at the back face, if it freezes, as at a core plug, or between a cylinder. There isnt an area of water jacket in your engine thick enough to resist the power of expanding water if it gets cold enough.