If it truly was 40k miles then it would be most likely valve seals, if 140k then either rings or valve seals, if it smokes or smells more on hard decelerrations then it is most likely valve seals, if it smokes or smells most on accelerations or when you first fire it up then likely rings. Unfortunately both are not trivial fixes, to replace the valve seals you need to remove the head and replace the head gasket and freshen anything that needs freshening (valve springs, resurface head, etc...). To replace the rings you need to do a complete teardown of the engine so that is a complete rebuild.
If you can tolerate the smell and can keep an eye on your oil level you can drive it like this for a long time before you need to address the issue, alot of people do that with these cars and they don't seem to mind. If it is the valve seals it helps to push in the clutch when you decelerate (less vacuum, less oil sucked in around the seals) and you will burn less oil.
Since you have a '76 in California and need to get it smogged if there is smoke the tester may fail you based on the visual but burning oil in my experience doesn't usually trigger a failed test unless it is really bad.