[1QuickS]

A little lean at cruise is fine. You can try opening the idle mixture screws a bit to see if that helps or perform "Lean Best" adjustment at 1500 RPM to help get idle mixture right when throttles opened up a bit. You want enough richness so that when you apply throttle at very low RPM the engine will take it and not hesitate.

I had 52's (!) for idle jets in my 2.3 with S cams but it is twin plugged. I now have 60s but I'm trying new throttle plates with thinning near the edges that sweep past the progression holes; this allows more air into the mixture than with when using constant thickness plates. I think 55s should be good for you.

I still do not understand the heating issue, I would expect a constant 180 temp in 80 degree ambient air during street driving.