Alvin,
The idea that those plugs are for freeze protection is urban legend. They are actually core plugs. That's where the pour the sand out of the casting moulds when the engine is being formed. They then have to plug these holes because it was the water jackets that the sand formed. They will pop out if water does freeze because they are a weak spot, but won't protect the block from cracking. I have an old 305 that froze with a 10" crack down each side of the block to attest this,
Scott
