I have installed several "engine Guardian" digital units on family
vehicles & are doing the same with my 3GM30f. Easy to fit and measures head
temperature instead of water
temp so there is less delay. (if you put sensor
pressure uses OEM sender on the TD's don't know yet what I have to do for the Yanmar. Probaby has normally open circuit with closed to activate alarm
. Has user configurable set point alarm
Engine Guardian EG3C Watchdog Temperature Coolant Sensor Gauge Overheating Alarm | eBay
If you insist on analogue, any automotive aftermarket store will have a suitable gauge(s) on offer.