I've read that LA-built cars' unibodies had black undersides as opposed to other plants using a grey color; maybe someone can confirm or correct this. Cars intended for CA sale generally had different advance timing curves, distributors & carbs, air cleaners were often the snorkel ("silenced") type, chrome tailpipe tips were omitted (except some Hemi Bs), and in some years had closed-loop fuel tank venting. Cars intended for high altitudes (Denver for example) also differed in some tune-up specifications.
The Calif Air Resources Board (ironically, "CARB") started dictating changes with the '66 model year, and noise levels were legislated starting in '68.
No doubt there were exceptions: I've owned both silenced & unsilenced air-cleaner '68s & '69s, and I can recall seeing a couple brand-new Bs with chrome tips during that time. Some laws took effect Jan 1st, others were model-year.