Back before I left Commiefornia to move back home to Tennessee in 1980, an upgrade to a smog-controlled engine required the vehicle to meet the standards for the engine, not the chassis. It's possible the rules have been modified somewhat since then, but generally installing a later-model engine makes it necessary to jump through a bunch of hoops. You could always claim the engine is an earlier model, but a sharp inspector will check casting or serial numbers.
Jerry
