Can Smog check results point to actual problem?

My 1977 half ton 2wd 350ci 350 turbo automatic Chevy pickup failed smog check as Gross Polluter. Could the numbers on the smog test point to actual
problem such as air/fuel mixture, unburnt fuel, oil consumption, bad compression, bad cat? Or wrong timing, unburnt fuel, oil consumption around value stem seals, worn guides, valve seating, piston rings frozen to piston, EGR plugged, carburetor adjustment, etc or are they vague? Of course, check of spark plugs is the first check. Check of compression is good and within 5% on all eight cylinders. If the cat is the problem, is that caused by the wear or mileage of engine? This engine does not have the hardened valve seats. In need of head overhaul or complete engine overhaul?
I'm ready for a newer vehicle but hate to part with it if repairable. Registration and insurance is cheaper than a new vehicle. A major safety concern is the fuel tank outside of frame rails.
Mr Goodwrench is not old enough today to know what a carburetor is. I took my 1975 Van with maximum speed problem of 20 mph, he wanted to rebuild (no parts) or replace (no replacement available) the carburetor. I returned home and replaced the $1 fuel filter. I can still get rebuild kits at any local auto parts store.
Should I take it for mechanic diagnostics since there is no computer in this vehicle?
Gary
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What were the exact results of the test? How can anyone point you in the right direction without knowing what part of the test failed?

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Yes.
Yes.
There is no such thing as a silver bullet.

Depends on which gas(es) were out of spec.

They don't last indefinitely and excess engine oil will tend to poison them.

A cylinder leak down test would provide more conclusive .

Well then, sounds like you want a new vehicle.

Not necessarily true.

Point?

If you can't diagnose it yourself, yes. Just because there is no on-board computer doesn't mean that diagnostics can't be done.
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