The Mig never had the design feature due mostly to the steel construction. The Blackbird was built of titanium which expanded in size with increased temps (and actually got stronger over time due to the heat). I do know that after missions the canopy would be almost 600*F and they had to wait to exit the plane due to the heat.
The SNJ has always been one of my favorite WW2 era planes (after the P-51 Mustang and the F8F Bearcat) I've never flown in an SNJ, but have flown in a T-6
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