If you have a head gasket leak, you should be able to detect it by blipping the throttle and holing your hand near the head gasket to feel it. From what you described, your carb is OK. I wouldn't go there yet. Try to find an exhaust gasket ands start there to see if it helps. When the truck is running and making it's sound, watch the distributor look around at the linkage for the advance to see if it moves. If you see it move, see if you can isolate it to make it stationary and see how it runs. Keep us up to date.
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