It's been a while since I sold my 4.3, but I THINK the rear freeze plug
was above the oil filter attachment and the front one if I remember
correctly was behind the water pump. Don't quote me on this, I would
look into it a bit more since I'm not 100% sure, but I do remember them
being around those locations.

Good luck with it! Are you replacing them because of a coolant leak?

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