Remember the purpose of the NACA report. Some US engineer during WWII decided that we needed to run the B-24 Liberator LOP to get the range AND increase the bomb load. Some General said, "That's ridiculous, everyone knows that leaner mixtures result in higher exhaust valve temperatures." The Top Secret study was undertaken to prove or disprove the adamant General's position. The general lost. The physics won. Along the way, it was discovered that EGT and exhaust valve temperature were not directly related as initially assumed. It looks like it might, but the red herring was chewed by researchers until we realized that valve temperature is most directly affected by CHT. Period. We also learned that there are actually mixtures where the exhaust gasses blasting past the exhaust valve were actually COOLING the valve. Depending on other factors, if one sets the mixture at 40dF ROP, the exhaust gasses can actually cool the exhaust valve! Try that fact on for size.
It's also worthwhile to note that science has the habit of slaying a beautiful hypothesis with an ugly fact.
(FWIW, the B-24 was the only airplane of WWII that was run LOP in cruise. It seemed to work quite well as it carried the highest bomb load the greatest distance.)