According to everything I can find the capacity of a big block 65 Corvette is 5 quarts, I would be leery of running it much under 4 quarts, so if you do this watch it carefully.
Agree with post 38.
Oil in the intake is a clue, need to figure out how oil is getting there. The very first thing i would do is pull the PCV valve (and breather hose if so equipped) and put vented breathers in the VC, You'll have to cap the PCV port of course. and see if my oil consumption continued as well as if pooling in the intake continued.
Monitor valve covers for oil coming out the breathers.
Results determine next steps...