I believe the stock timing is 6 degrees Before Top Dead Center (BTDC), which is a setting that is needed as part of the effort to help minimize emissions from an engine. If the timing is advance "too far"it could cause the engine to increase its NOx emissions due to increased internal combustion compression at the time a spark plug is fired. Often there is a point/counter-point setting the initial ignition timing setting where performance increases cause NOX output creation, something the 6 degree setting helps prevent - at the expense of performance. But going into too much initial advance will cause problems also. The objective for a dynamic timing setting is to get high performance out of an engine irrespective of the engine's emission output. So, for street engines a 6 degree initial timing setting is often correct.
The optimum initial timing will depend on a lot of things, to include compression ration of the combustion chamber in the engine, Octane level of fuel and any additive in the fuel (to include ethanol), Total in interim levels of (dynamic) timing advance whether caused by the vacuum advance, centrifugal, or aftermarket electronic advance sub-systems, engine load, timing gear stretch impact, engine RPM, temperature of the engine, air/fuel ratio, etc. With decent gasoline I find the initial timing being set to 12 degrees begins to wake up most engines. Setting your ignition up 12 degrees BTDC may, however, be too high if you are running a low octane of fuel, have relatively high compression in your engine. If you hear pinging you need to back off the timing until the ping is minimal or gone.
There are several "old school" ways of ascertaining your initial ideal timing. Some require the use of a "chassis dyno" that can add a load to the engine in a manner similar to road conditions. The way I used to do it is simple, and showed to be plenty good for "seat of the pants" timing adjustments.
I would leave the distributor hold-down clamp slightly loose so I could adjust ti, but not so loose that it would turn from the distributor housing on its own. Then connect a tachometer to measure engine speed. I would then leave the vacuum advance hose connected to the port vacuum source. Then using the chock high speed idle cam I would run the engine up to 2,500 RPM. At that point I would begin to advance the distributor position to increase (or decrease) the timing until I hit a maximum RPM reading. Once I hit the maximum RPM due to timing adjustments I would back off the timing advance enough to drop 200 RPM from the peak RPM.
Once the timing was set like that I would remove the distributor vacuum advance tubing, and check on the timing advance reading, For me it was consistently 12 degrees, but your engine may well be different.
Of course, I intend for this technique to be used for vehicles being run on a private race track. For engine on the public roadway you are going to have to comply with emission control requirements of your state and the federal government, to include engine tune settings. Many states no longer require any emission control equipment to actually function after the vehicle is 25 years old (check on your own state), but in some of those states the emission control components are not supposed to be removed or tampered with.
Also, please note, not all emission control items are "bad or will decrease performance. Positive Crankcase Ventilation (PCV) systems are good to have. Likewise the fuel evaporation control systems work well and do not rob horsepower from an engine. Some Thermal Vacuum Switches (TVS) units work well with engine vacuum advance systems, and in fact could be helpful in preventing engine overheating. I have a quick YouTube video explaining how those TVS units work, at the following web site:
