Well you and a lot of other guys have looked at total advance that way, I even see them doing that in magazines sometimes, but its not right. For Total advance which is usually around 36 (plus or minus a couple) total crank degrees for any engine,,,chevies included your talking about centrifugal and initial only so yes your vacuum advance should be plugged. The reason they do that is that vacuum advance is load dependent ,, at WOT you will not see any vacuum advance. It is important to find total advance(its just a term) on the dyno for an engine because on the dyno you make wot runs and you vary the timing until you get optimum torque(which is also optimum HP at that rpm) at all the given rpm ranges. Then the factory takes out a couple of degrees to be safe and calls it Total advance and they program their centrifugal advance to stay within that. When charted out its a fairly steep curve with all of it in by about 3000. When you design a spark curve you look at WOT runs for the best centrifugal spark and then you look at part throttle runs on the dyno to see of your in the ballpark for vacuum advance, but generally the curb on part throttle spark is "ping" ,,,and at the factory we referred to it as octane requirement. We would run octane requirement on a given engine and advance combination and they would come back and say 95 octane,,and we would have to start over cause thats too high. It cant all be done on the dyno. But there are other ways to affect octane also-we found that 10 degrees higher air inlet temp upped the octane requirement by one point and thats one big reason that we went to ducted inlet air,, to get away from engine heat.
A racing engine has no need for vacuum advance because you arent racing at part throttle anyway you racing at heavy loads and wot. IMHO every (old tech)street engine should have vacuum advance with the exception probably of blown engines like yours because blown engines are very sensitive to detonation and transient spikes from vacuum advance could do you in, and also your controlling your peak pressure by the blower so timing is less of a HP issue and more of a detonation concern. Another couple terms ,,,"ping" and "detonation" are two different things. Ping refers to a second flame front hitting the one already started by your spark plugs ,,,it causes that "ping" sound, thats the collision of two wave (pressure) fronts in the cylinder. Detonation on the other hand is when the cylinder charge fires on its own due to pressure and heat without the plug firing,,,ping is only mildy troublesome, detonation is bammm your piston is gone almost right away because the pressure is so high.
The newer generation of blown engines or turbo engines can use computers and ping sensors to sense too much spark advance quickly enough to knock it back before it becomes detonation. The new computers map all the possible combinations of engine load and throttle position and heat and can tell whether unburned Hydrocarbons are in the exhaust and adjust parameters so fast that its almost impossible for a carburetor to come even close to their efficiency.
sorry thats so long,,, ya get wordy as ya get old I guess