Some basic info from the aircraft mechanic.
Temp instruments and their senders are a matched couple. Viglia gauge and Viglia sender. It could care less and doesn't know what engine it is installed on.
I am guessing that Viglia who has made gauges for many European cars did not have a temp probe that fit a US 1/8 in. pipe fitting so Ford added resistors (a patch) so their probe would work. Dropping the gauge feed voltage by using a resistor will work but not give accuracy through the full range.
If you are seeking super accuracy the way to go is to send the gage and sender to a instrument repair shop. They can set you up with a gage / sender combo that will give you an accurate temp reading.
Chances are with the 40 year old wiring, gauge and patched together sender you will have error in the reading. I have used West Valley Instruments in the past with great results. My instruments come back looking new and working.
The Temp switch (EPS ?) was used on dual diaphragm distributor to retard timing at idle to reduce hydrocarbons. It ported man psi to the retard diaphragm and that retarded the timing. If you are running an MSD ignition then it's of no use. Don't they have programmable electronic spark advance ?
It would be interesting to know just what that switch is wired to . Are you running the original 4300 carb with a throttle solenoid for fast idle ? I think that is the power feed take off for the switch.