Pieces of steel in cylinder??

sireland67 said

Replace them, they are cheap, they rot from the back side, where you cannot see the rust.
Just sand the edge of the plug, and the block with 180 grit sandpaper, use permatex, and install with a large socket, they are easy to do.
Mancini Racing Brass Freeze Plug Kit

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You will be glad you replaced the frost plugs, especially the ones on the back side of the engine. They will start dripping after 45 years and that would really tick you off when everything is bolted together.

Pop the old frost plugs out and you get a chance to clean the rust scale out of the bottom of the water jacket with a heavy wire and small tipped vacuum cleaner. Now the new engine will cool better too.