I have a '76 SLC, also live in La-La land, and have done the following to keep her cool.
Had the radiator cored - not just flushed.
Used RedLine Water Wetter.
Had the engine steamed cleaned - twice !!
Bought the car 2 years ago and did a full-on tune-up myself (vaccum lines, plugs, filters, timing, etc etc) so I know its done right. Damn thing, with 130K sure runs nice.
I also use Premium only.
Anyways, my temp has come close but not past 200 degrees (your car reads in centigrade) and only runs hot (190 degrees) at 80 MPH and full A/C on the highway.
As far as your ventilator blues (old blues song - see Exile on Main St.), check the plastic cover over your blower box for cracks and replace if necessary and you may want to have the heater valve replaced for kicks. Mine was leaking a little, both externally and internally.
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