What are the chances of an old car passing smog test?

I have an old Ford ranchero 1978 and I put money into fixing it my mechanic checked out the engine and fixed all the problems and I just need to know does it lower the percentage of passing smog just because it's old

In most areas I'm aware of a car that old is exempt from testing.

There are some areas where it must pass, but only using the standards of the year it was built.

If it is in proper tune, it should be fine UNLESS it has had any smog stuff removed.

Most states don't ( can't ) check anything over 25 years old, because they don't have room on the inspection computers for the specs anymore. But, either way, the car would be checked to the pollution specs in existence WHEN THE CAR WAS MADE. So it would be checked against the 1978 pollution specs, which were quite minimal…

Where I come from it is called an exhaust emissions test.
Google the authority in you area. Most questions I have asked them were resolved in 20 minutes or less, with a phone call.
It is discussing it without providing the proper info that will confuse the issue.
If you can buy tabs without getting sent for a test then go do what you want.
In my experience, old emission parts that have failed can cause more pollution than if they were never produced.

Very good if you add a hydrogen cell to get better mileage and cleaner exhaust numbers!

They put a stinger in the tailpipe to check hydro-carbons your car is pre smog equiptment a simple carb mixture adjustment will bring it into range easily no problem i'm surprised you don't have issues with non leaded gas? Somebodys done some modification to your heads it'll pass ez