[NC_John]

State and federal laws usually dictate that the emissions must be as was applicable for the model year of the vehicle, not the engine.

BUT - Can you get a tuner (a bullydog for example) for the engine you are contemplating? Usually you'll have to program out the EGR, DPF, DEF (done by installing an "off-road high-sulfur" tune) to remove that stuff and keep everything happy. Otherwise the computer will be eternally pissed off and you'll probably be constantly dealing with MIL lights and derating issues.