[lust4speed]

Take the thermostat out while you are working on the problem. My friends and I have probably tested over two dozen Pontiac engines and none of them ran hotter with the thermostat removed. There is enough restrictions in the engine and cooling system that the coolant cannot travel "too fast". In short, no thermostat and a perfectly working thermostat cool the same. There are other good reasons for running a thermostat but for testing you can't beat simply removing it and having one less variable.

You mentioned belt squeal earlier in the thread, and that would be a sign that the fan clutch is working properly. Use a good quality belt adjusted properly and you have removed another possible weak point from the testing process.

Use a known good temp gun to verify actual coolant temperature. For example, Stewart Warner guarantees their gauges to be accurate within 10° of reading. That means that an engine running an actual 190° can have the gauge read anywhere between 171° and 209° and it is within spec. Anyway, getting a second opinion might prove the gauge is very pessimistic. Now take a Chinese gauge and it can literally read anywhere.

Pontiac used a massive amount of different pulleys over the years, and for that matter even for a given model year. My '67 and my friends '66 used a 1/2" belt for the belt that went around the crank, water pump, and power steering, and a 7/16" belt that went around the crank, water pump, and alternator. In Gates terminology this would be an XL 25 belt that started with a 9 for the 1/2" belt and a 7 for the 7/16" belt. In my car's case, it took a Gates XL 25 9520 for power steering and a Gates XL 25 7490 for alternator. The different belt widths matched the pulleys with the wider groove in front. Not all years had the staggered widths.