LOL, piston are in the combustion chamber and would see some of the hottest temperature and they do not get anywhere near five hundred degrees... Exhaust valves get hottest because the have no place to shed heat and are in the middle of the exhaust flow.think part of the problem is to only focus on the melting point of the metal. We need to look at the strength of the material over temperature. While aluminum (beer can or turkey pan) will melt near 1200F,
How often do you change your pistons? Aluminum heads...
Oils @ 300* begin to breakdown
The crossover never sees the exhaust temperature ... shoot it with a heat gun.
A blocked crossover stops the flow of exhaust into that area of the head from the exhaust pocket hole 1/8"-3/16". Gasses like water find the easiest path out.
+1SCE gaskets and Mr. Gasket both sell intake gaskets with blocked heat crossover. I confirmed several years ago that the gasket will not burn through at the heat crossover. Chuck