In this case the law has already been written. It's not a CARB-approved, nor EPA compliant engine. You're not allowed to run it on the street. The law is written so that everything you do to a car's emission system is illegal by default. To make any engine modifications in California, the part must be CARB approved and have a compliance sticker on it. Engine swaps in California are legal, as long as the engine being swapped is at least as new as the engine in the vehicle and meets the same regulatory requirements. Which means you swap in another EPA/CARB approved engine, but not a jet engine.