SLT-6 is 0.060 Over - Runs Hot...Why?????

Not the .60 bore. I'm thinking water circulation around the engine.

Flush the block properly, have the rad pressure tested and checked for flow at a reputable rad shop, Check the thermostat for proper opening by putting it in water and boiling it with a thermometer alongside it. ( 180 degrees if I recall ). And , as was suggested, check the water pump impellers as this engine did sit for a long while.