The big heat-crack on the right manifold can make a sound like a clack or knock.
From the pics I saw I was proven wrong about the rocker stud :rolleyes: :o
The unit on the right manifold is a heat sensor for the auto choke on your carb smile
Have you replaced the plug wires?
The heads on your truck
462624.....75-86...350/400......76cc chamber, 1.72/1.5, 1.94/1.5 or 2.02/1.6 valves

There is enough good in the worst of us and enough bad in the best of us that it does not behoove any of us to criticize the rest of us.
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Be yourself. If you are ever lost, It will be much easier to find yourself if you know who you are!