Before spending money on a gauge, you could check that yours makes sense first. I am lucky enough to have a friend in HVAC business with one of those laser guided, hand held temperature sensor deals. You can check just about everything with one of those: manifold temps, head, rad, water pump, hoses, block, a dogs butt....

Might be a good idea to check timing and air fuel if you can. Those things, when incorrect, can cause an engine to overheat even when the cooling system is spot on.