I had the same problem on a sb engine. But leakdown showed around 18%. It was a bent valve. When you have the leakdown tester installed just spray soapwater around valveseats (intake removed) valve guides etc everywhere you would expect it to leak. I dont think your problem is in the cylinders they need to be really worn/damaged to leak that much oil. And i dont see the pcv eating up that much oil either. Do the leakdown thing then make yourself 100% sure its not the intake gaskets. If your carbs are a little rich it will wash the runners from oil so you wouldnt see much there.