Quote: So with the timing set at an 'indicated' 5 degrees retarded, it didn't ping. At TDC, it pings when it's hot. At 5 degrees advance, it pings a lot, so it looks like we have a pattern here & I would recomend against setting it at 10 & 15 degrees advance as it doesn't take Einstein to figure out the probable result.

Dattodevil is correct, so lets get back to basics. How do you know that the piston is actually at TDC when the timing mark lines up. Best to pull the plugs & slip a cane chopstick down number 1 plug hole & turn the crank very slowly with a long bar & socket while holding the chopstick gently in your fingers.
You will soon get to figure out when the piston is at TDC. This is not 100% accurate of course, but do your best, & if the mark is way off, then that could be a problem & a small dab of white paint to make a new TDC mark would be a good idea.
If the existing mark is accurate, then it's time to look for other causes, but make sure that this is right first.

The default position for the vacuum canister is in the non-advance position & it only advances when you are at light throttle, so at worst, it will remain in the 'at-rest' position & not provide any vacuum advance at all, even when faulty.