89 360 engine

Grab the crank pulley and see if it will turn over. rock the pulley back and forth and listen for any bearing noise. Unless you can hear it run and see the oil pressure, I'd figure it to be a core. Tear it down and at the least, do a ring, bearing, and reseal job. I'd probably do a valve job too depending on how everything looks inside. Once you have the heads off, you can pour some solvent or gasoline into the ports to see if you have any valve leakage. I'd still pull the valves, lap them in, and install new seals and brass freeze plugs. (in the block too!)