Blown Head Gasket or Cracked Block

Retorque the head bolts. Be sure to do a quick run through on the valve lash clearances after doing this.

A little ways back I showed that NOS gaskets from 30 years ago are still being sold. NOS distributor gears from 40 plus years ago as well. So unless you pull the head there is no way to know if a modern no-retorque gasket was used even if the rebuild was done last week and the rebuilder did not specifically check the gasket. Oil from the head bolt passages at the rear of the head can seep down next to the water passages there. If this is it, then you're lucky you noticed it before the gasket gave out at the fire ring.

Good luck.