Iv'e ponder this for a long time. Is there a ideal operating tempature for the slant? Reason being my 225 runs at 175-185 dgrees in city traffic all the time. Will sit at idle for extended periods of time in +100 degree and not exceed 195. Using 185 degree thermostat with a 3-core radiator and auto trans with stock fan blade and no shroud. Also using Auto Meter gauge and sender, have used others to verify reading with no changes. Total timing is 34 degrees with vacum advance operable and this is with a motor last overhauled in 1972. Not complaining, just curious.

Sounds like you have a good cooling system that is working well.

In general, the cooler you run the engine the less wear you get. (150 -160 minimum temp.)
Run the engine hotter and get better MPG and a cleaner burn. (less smog)

The Slant came from the factory in the early years with a 180 thermostat and by the early 70s that was increased to the 195 degrees. A SL6 head tends to run hot on the front cylinders because of the way the coolant flows through. (#2 is usually the hole that detonates first when all compression is even)

The trend I see is that new cars run even hotter engine temps, around 210 but these engines also have more thought put into keeping the cylinder temps very even, in order to prevent hot cylinders and detonation. New engines use "reverse flow" cooling where the head(s) gets coolant first, usually introduced front and back of the head to keep temps even.

For our Slants, I know my drag car runs the fastest when I stage it in at 180-185 and it's at 200-210 at the end of the pass. For a street car, if your cooling system can safely keep the car at the thermostat temp. then run the temp. as high as you safely can. ( doing this reduces your safety margin before boil-over / overheating.
DD