Wanted to share my experience in case it's helpful to anyone out there. Car is a 1990 IROC 350sbc 5spd. According to the temp gauge the car always ran hot and routinely read 240-250 degrees. It never actually overheated. Mechanic, whom I trust and has worked on the car a couple times already, checked it out and measured the engine temp reading with a diagnostic computer and temps at other various locations with an IR temp gun. All readings came back well within normal. So analysis shifted to the instrumentation as the engine was running at normal temps. I had the gauge cluster replaced last month so it was highly unlikely the gauge itself was to blame. Plus the new gauge was reading the same as the old gauge. Conclusion was that the heat coming off the headers was affecting the temp sending unit leading to higher than actual readings on the gauge. Tried wrapping the sending unit with insulation tape but that didn't help. The solution we went with was to install a resistor between the sending unit and the gauge to adjust the temp reading down closer to actual. I know there are alternatives like replacing or coating the headers but this is the solution that fit my budget.

 

That's just putting a band aide on the problem.The solution is to move the temp sensor away from the headers