also make sure your sparkplug wires are not hitting your exhaust manifold or headers if you have them. if one of the wires is touching it will melt and cause your truck to have that symptom.
Do you know of a good mechanic that can work on the old stuff? Maybe go to a car show or join a classic car club, the members will be more than happy to help, I bet. Your problem is likely easy to diagnose, and maybe to fix, for someone who’s worked on cars with carbs and points.
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Came here to post exactly this, @texases beat me to it!
It is so stupid, I worked on those old cars growing up and could fix anything, I have been looking for a hobby, maybe this is it, got feeler gauges dwell meter, timing light, hard to think someone would need my skills to replace a vacuum advance rebuild a fuel pump carb etc. Even seen posts sorry you have to pump the gas peddle to set the choke on the carb, Ready to rip off the rich idiots.
It’s premature to be thinking of a rebuild BUT, it would be a good idea to run a compression check first on all cylinders. It would be very easy (and often done) to throw everything in the parts inventory at it while trying and failing to fix an internal engine fault.
This engine spent most of its life running on leaded gasoline and lead in the gas (as compared to unleaded) creates deposits on cylinder head valves and seats which can lead to compression issues. This issue is non-existent on unleaded gas engines.
My gut feeling is that plugs and wires will fix this although if there is a compression problem on that cylinder the problem will likely reappear at some point after killing the new plug.
Cool truck and great engine by the way… 
When we had similar symptoms happen to our '90 Mazda Protoge years ago, a misfire that turned into one cylinder not firing at all. With a new set of plug wires it ran like a dream. However it happened one of the plug wires was wrapped in electrical tape to try to cover up a broken wire, when the shop foreman found out he insisted on paying for a new set of wires since the car had just been in on the Friday before for a nose to tail physical at 160,000 miles.