1977 inline 6 vs. california emissions

[moregrip]

I should be taking delivery on a 1977 250 inline 6 shortbed stepside here soon.
I know it's not emissions exempt in CA, ......anyone know how clean these motors typically run? from the one engine pic i have it looks like it might be equipped with federal emissions which I believe for that model year was the same as california emissions.

I plan to do all the normal maintenance, plug wires, plugs, oil, filter, fuel filter, air filter, pcv valve, any water or vacuum hoses, etc etc.

If it doesn't pass smog what are the typical culprits? where would you start?
thanks for the help