Simple, it is called math, physics and efficient design. See in the modern world we understand that aluminum is a better heat conductor than a chunk of cast iron, that bigger and better designed intake and exhaust ports/valves flow more air, that combustion chamber design equal more horsepower/mpg, that aluminum is lighter than cast iron.
The Jeep 4.0L cast iron head is a relic of the past, it traps heat and sends it to the radiator for rejection, heat that the Edelbrock head sends down the exhaust or radiates or convects from the surface of the head. The Edelbrock head more efficient combustion chamber designs allows higher compression and better fuel burn which equals more power and better mileage.
The Edelbrock head is the cheapest way to more power and better efficiency for your 4.0L.
Don't be that old dog that can't learn new tricks.