All automobiles sold in the US since 1966 have had federally mandated emissions equipment installed, and by federal law it cannot be removed or altered. Period. I'll bet your 1967 Mustang is not in compliance with federal law. And the heads on your Pantera do not have CARB certification.
Cars in California older than 1975 are free from annual or bi-annual visual inspection and tailpipe emissions testing, but the state cannot reverse a federal law that mandates nobody can alter or remove the smog equipment mandated by the federal government for that year. This is what many people don't understand about California emissions law, older cars are exempt from inspection and testing, but they are never exempt from compliance. The equipment is supposed to stay on 1966 and newer vehicles forever.
The smog shops who try to help enthusiasts are just that, they are business owners trying to help enthusiasts. The kind of shop the average Pantera owner would go to for assistance are owned by good people, not criminals; but by the letter of the law they are criminals. If California informed you tomorrow to take your 1967 Mustang or your 1972 Pantera into an inspection station within the next 30 days, what would you do? Those vehicles are not exempt from compliance with federal law! Wouldn't you start looking for a sympathetic smog shop? I would have to do the same. And we would patronize those shops because we expect the owners of those shops to violate the letter of federal law to help us keep our cars on the road.
In my opinion, if a car passes the tail pipe emissions test, it doesn't matter what equipment is installed on the motor. The spirit of the law is being adhered to, if not the letter of the law. It is fairly easy to tune older cars to pass the tail pipe emissions test. But tailpipe emissions is only half the picture ... is your car's evaporative emissions equipemnt in good order?
-G