quote:What does the needle's reaction tell you?
It would tell me that either the ignition system lost power or the triggering device (distributor points or electronic sensor) was not functioning properly.
quote:What would the vacuum indicate to you?
It would indicate that the primary distributor wire (or the ground wire) inside the distributor is not making contact when the vacuum advance moves the breaker plate inside the distributor. An insulated wire could have a break in the conductor, but not in the insulation. Pulling on the ends of the wire will pull the conductor apart, and the insulation will stretch and shrink (slightly) into the void (clue). This type of break is hard to find. Or the ground wire inside the distributor could be loose.
There is always a possibility that you could have a severe restriction at the fuel entry to the carb. I have seen needle seats slowly unscrew to the point that the float is virtually at the bottom of the float bowl. This forces the needle valve to be bottomed in its seat, letting little or no gas into the bowl, and certainly not enough gas remains to function properly, other than to allow the accelerator pump to be able to suck up and deliver a shot of fuel out the discharge nozzles. Car starts and immediately dies. Don't ask me how I know.
Old gas can certainly be a problem, but what usually happens is that the engine will either be very difficult to start or will not start at all, not even one sputter. If you squirt (or pour) a small amount of fresh gas down the two primary bores, the engine will start instantly and will continue to run. In some cases, a second "primer" squirt is needed. Once the engine is warmed up, the engine will continue to start and run normally for the rest of the day, as long as the engine doesn't cool down very much. Once the engine has cooled (especially overnight), it will not restart unless it gets a squirt of fresh gas. Ask me how I know.
John