Later model Chevy 6.0 Liter engine are not equipped with an EGR system. Instead these engine models are equipped with catalytic converters and unique cylinder head design which allows for adequate NOx reduction without the use of an EGR valve.
Both engine designs from the exterior appear to be the same except for engine head design, catalytic converters and computer firmware programming. California will not allow the replacement of the current engine with a non-EGR version unless you replace all the emission components belonging to the new engine, including the computer module. Your best bet is to replace with the exact model year and design of your current Chevy HD 6.0 liter engine.
