How I remove them is use a large screw driver or chisel and a hammer, hit one spot until it rotates in and twists inwards then using slip jaw pliers/vise grips hook and pull it out. Clean sealing edge in block with sand paper, coat block and freeze plug with sealant (NOT rtv type one, of my choices would be Hylomar or a sealant which dries hard).
Start the plug with in the block with a large hammer/mallet and a socket which fits nicely inside the plug.
Once the plug has started squarely in the block-- IMPOrtant -- finish with a socket that is slightly larger than the plug.
Reason for larger socket...
1. When using inside socket can have stretching effect and slightly reduce outside diameter therefor making plug not as tight in the block. Not good.
2. larger socket stops hammering it in to far because if is larger than the block hole.
It is one of those jobs where a large hammer is better than a small one, it take a lot of force to start it squarely.