The iron vs aluminum cylinder head argument is over.

intake valve in heads
Mopar Chrysler 318 360 1.600" +050 11/32" Stainless Steel Exhaust Valves

exhaust valve in heads
Mopar Chrysler 318 360 2.020" +050 11/32" Stainless Steel Intake Valves

I have those valves in the 360 that is our 75 Duster that is being bracket raced.