So, when did the six pack come out?

I'm thinking after the 195 thermostat.

With the gauge "bouncing around" I'm thinking the issue isn't coolant temp. The water temp gauge is slow acting, takes time to heat all that mass up. If it's bouncing the issue is in the gauge circuit. Is this a mechanical gauge or the factory one?

They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.