How long this engine has sat without a start up is completely unknown.

Thank you for the ideas! Today I will rig up a temporary way to run the engine for extended periods. I will perform your overfilled crankcase procedure as well. Perhaps ACDelco GM engine cylinder/combustion chamber cleaner will find its way into the engine as well. After a while of running and flushing the cooling system I will perform another compression test alongside performing a leak down. Lets see if I can't get to it before the rain falls.

Ill come back with an update

Side note - I've heard Valvoline VR1 Racing oil is preferred for our old blocks due to their zinc additives. Would anyone have anything to say for or against that oil choice? Thank you!

SGM