Ed Anderson wrote:

Anything you can do to reduce the power and therefore heat your engine is developing will reduce the BTU of waste heat your cooling system must deal with.  Leaning would reduce the heat load - but, whether sufficiently to materially affect your cooling is another story.  My calculations shows the following:

Rpm    A/F ratio    Fuel Flow   BTU
1000   12:1            2.9            1417
1000   14.7            2.3            1157
1000   17.4            2.0            987

However, keep in mind that at lower  idle RPM  you need a richer mixture to keep the engine turning over, so you can not lean the engine as much at idle as you can up in the air at cruise.

My 0.02 worth

If it were possible, cutting the BTU by 30% would just have to help. 'Course, that's just an semi-educated opinion.  I was thinking a little more throttle and a little less fuel, with the goal of having the excess air carry off a disproportionate amount of heat. I've heard you say that in cruise you can use the mixture knob to very effectively control power. Why not on the ground?  Set the throttle to quarter or even half open and bring the mixture down till it will barely keep turning.

Note:  I still don't have an engine running, or I'd be experimenting with this myself and reporting the results.