Your setup is correct for 67, however GM later changed the design to the closed breather system due to the very same reasons you are experiencing, and for emissions reasons. The later design has a breather element in the air filter housing, and a tube running to the valve cover. When at WOT, the closed system allows all the oil vapor to just enter the carb, so there is no oil mist on the valve covers and the driver wouldn't smell oil at WOT. To remove the problem, you can go to a sealed air filter housing with the built-in breather design, or purchase some aftermaket valve covers with better oil baffles for prevent the oil from exiting the breather. What ever you do, don't replace the breather with a plain cap. The breather is the crankcase's fresh air source to replace the air the PCV valve is sucking out.
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