68 temp gauge-2 questions

My temp gauge starts out all the way on the left in the cold area, over the course of about 15 minutes it will make it to the middle. By the time I am driving about 1/2 hour it moves all the way to the hot side. The car runs great, and I verified the actual temp with a Fluke digital thermo that the highest reading I got at the top radiator hose was 193 degrees. QUESTION ONE, is there any way to adjust the needle reading? Could you put a resistor in the line to adjust the actaul reading back to the gauge? TWO, I can't find a replacement gauge anywhere, like CJ etc. Anyone know where and if they are available?

I bought the sending unit from AutoZone and it looked just like the one I took out. My car did something yesterday that it hasn't done before though! When I got back from a two hour ride, I noticed I had steam coming from the bottom of the catch can. After letting it cool down, I checked the water level, and it was below the fins in the top of the radiator. It took a half gallon of coolant to bring it above the fins. My cap is rated for 13lbs. Is it possible that it is bad, or should I be running a higher rated cap? I ran it after I filled it with the cap off and the heater on to check for air, but I never saw anything. I waited for the thermostat to open, and still nothing strange. I was thinking head gaskets, but it runs great and I never see anything unusual out of the tail pipes.

I thought that if my oil pressure and voltage gauges seem to be reading normally that it would not be the CVR. Some other questions I have read say it could be a bad head gasket, but I checked for coolant in my oil and oil in my coolant......nothing. No white smoke while driving, no air bubbles in the radiator while it runs with the cap off. I guess I should just buy a cheap temp gauge and see what it reads on something other that the old gauge.