340 has no balls

The line for the heater control wont casuse that , i would look more towards carb base gasket , pcv port it would be a big one possibly intake to head leak look for sucking oil at the gasket{ spray wd 40 while it running listen for engine to speed up} also check the timing chain play with the dist rotor rotate the crank pully by hand clockwise, counter clock wise watch the rotor ..more than a few degrees and the chain is toast possibly jumped a few degrees what is cold cranking pressure ? stock camshaft? like was said a big cam can do same thing