How do you adjust the timing on 1979 Caprice Classic?

That should be a 350 cubic inch engine with a carburator, HEI ignition with a vacuum advance. You will need to hook up a timing light to number one (1) cylinder. That is the front plug on the driver's side. Start the engine and let it warm up. There is an indicator on the front lower side of the engine. It is marked with the degrees. Disconnect the vacuum from the advance and plug it off and then adjust the timing to the desired specs. Tighten the distributor and plug in the advance. If you do not get an increase in rpm when the vacuum is connected, then the vacuum advance is bad.