[W403]

Although there could be many reasons for this, here are a few things to check. Considering the engine is in decent working order and knowing early olds blocks are pretty tough, try these recommendations. Ensure that the PCV valve has the correct vacuum rating for your application. If any components have been changed;camshaft, headers etc, you may need to experiment with different PCV valves by they're vacuum rating. PCV valve in one valve cover hooked to the correct vacuum source and a vent hose from the other valve cover to the air filter lid. With the PCV valve hooked up to the carb vacuum source check the PCV valve opening vacuum with a gauge and the engine running. I understand this does not compensate for engine load but will help dial you in on what vacuum it's opening at. Also the valve guides could be worn as well and causing blow by. As well, you may only need to either reinstall the correct valve covers in case the chrome units do not have an appropriate baffle for the PCV if yours are leaking at the valve cover connections. The latter being the simplest, and the one I have corrected on many cars some of which I had to use double gaskets for rocker clearance ( they were rubbing on after market units and no replacements available at time) sealing them overnight with aviation cement ( don't laugh, it worked..heh) and longer valve cover bolts. I also used an aluminum can to make a baffle so oil wouldn't get sucked up into the PCV and making it smoke which was the case for repair) Don't forget to use an inch # torque wrench if all possible and torque from center out per spec slowly, I've never had a comeback using this method and prefer it done right the first time. Good luck.