Couple O things,
If the guage is electric and reads low 99% of the time you may have an electron problem.
If you did not conferm the real engine temp. Is it overheating?
Back to the 99%. (and not for a protest) Is the thermostat opening and closing correctly.
One more thing. You and this thread is why I joined this group. Been hiding in the shadows for a long while. The Rambler brought me out. Back in the day when I worked for a living I got all the weird and crazy things to fix.
One more, more, thing. I am really an old guy just a new guy here. Don't give a crap about "PC" but I do resepct the other guy and his opinion.