When I dissassemble my 78SC's bottom end I found significant cuttings from the factory where they drove the steel oil line into the case (the one that goes from the thermostat to the oil pump). I'm no expert on their assembly but it looks like the pipe is driven into the case and when it passes through the aluminum it make these cuttings. In any event I has 3 or 4 good size pieces that were loosely attached to the case and came off with a light pick with my fingernail. Who knows how many of these already cam loose.
It's definitely an area that needs attention on a rebuild.