Grey smoke continued to be an issue and I pulled the intake manifold today. It looks like the bottom of some the intake ports are not sealing correctly. The gaskets are FelPro 1228. The intake is Edelbrock Torker. Cylinder heads are the original 351C 4V. I am trying to figure out how to avoid this again. Earlier I found that the four 5/16" bolts were not tight enough even though the got 25 lbs torque at installation. I appreciate your suggestions.