Will an engine bought from a 1999 Silverado originally sold outside of California pass California emissions

There are two type of emission classes.

Federal and California emissions.

Look under the hood for the emission class sticker.
Smog check station's machine in CA are programmed to handle both types.

You do not need to change anything before the inspection.

==== Side notes: You should check the service record for the last Catalytic converter,O2 sensors and EGR valve change.
Service interval for
Catalytic ~180,000 miles O2 ~150,000 miles EGR ~160,000 miles


If you can locate the last smog test (even from out of state) Check for the
CO NOx