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Buy a thermometer and check the guage against a real temperature with it just idling from cold for 20minutes. We blew a head gasket with the temp gauge reading half and no water left. That will tell you if the water is up to 80deg, if the thermostat is working, and the choke should or shouldn't be working. As the Spirit man said, the choke would affect all cylinders equally. A more interesting outcome would have been from swapping the plugs from 1 & 4 into cyls 2 & 3 and seeing what happened. All you can do is drive it and see how the new plugs look in a week.

It doesn't matter how big the radiator is the thermostat should regulate engine temp to an even 80-90 degrees at all times, so fit a thermostat as yours is faulty or missing. That will help you establish a hot running condition that is consistent and wont affect your test results. Engines wear prematurely if they never get to an even up to temp state for general use, as the pistons need to expand with the heat of the system to give ideal tolerances. Fouling plugs is usually a symptom of too much cold enrichment, a general rich state or incomplete ignition in that cylinder leaving the sooty deposits that block or insulate the spark from occurring in the correct way. So from what I can gather the issue was with cylinder 1 and now its with cylinder 4 as well. If it was a choke issue specifically you would see all cylinders affected in a similar way. Is your rotor button worn? Do you have the correct points gap? If its worse on the freeway then your issues might be being compounded by the rushing of air or the extra motion based forces that occur in this state. I once had a car cutting intermittently as I approached 100klm/hr. If I drove under 90 no issues, but if I drove over 95 I would experience misfires. I stopped on the side of the highway and saw that the wire attached to the ballast resistor was faulty, so I wandered over to a nearby house, asked for some tape, taped it on and drove home no worries. So look for loose connections in the ignition system, and check that your engine grounds and battery to body grounds are clean and well attached. I think were past expecting this to be a basic service related problem and its going to be something more obscure.