I was wondering the same. The Felpro gaskets are very thick and perhaps they are intended to help compensate for this type of issue. The thickness of the gaskets may have worked against me. During the current reassembly I noticed that I used thin washers on the the 5/16 bolts and they had deformed. Perhaps this was from heavy torquing later. In any case the gaskets and washers may have added to the problem by relaxing when everything got up to temperature and then shrunk after cooling. It is now reassembled with new gaskets, clean surfaces, and thick washers. So far, so good, During this I found a likely vacuum leak in the brake booster hose connection. And Doug has identified a likely carb float level issue and possible improvements in the PCV system. When the car fired up today it sounded better and I could not detect grey smoke. I drove it a fair amount without issues. My fingers are crossed.