As long as the vehicle, the motor comes out of is newer than the vehicle it is going in to and AAAAAALLLLLLLLLLLLLL smog components are installed PROPERLY; you can get it Ref'd in CA even if the engine is out of a GM vehicle without being a "Blue tag" or "kit car". Now the problem with this is the Smog Legal headers and exhaust manifolds dump directly on the steering so they have to be modified VERY carefully or the good ol' smog Refs will pull the rug out from under you
I am in the midst of trying to mod a set of SLP street legal headers on my S13 coupe to keep the Catalytic Conv in the "sameish" location but definitely same distance from the head.
-Shaun