If the breaker cam (what the contact block on the point set rides on and makes the points open and close) is worn, as it well might be, it will be nearly impossible to get the dwell readings to coincide with the specified point gap for the points. If a typical distributor is similar to the dual point distributor I have, some of the lobes will be worn more than others--which I checked with a dial indicator when the adjustment and dwell could not be set to where I wanted them to be. Same situation could be true of any point-type distributor, regardless of single point or dual point.
Dwell and spark timing are related also. Meaning that if the distributor position is not changed, dwell changes (I don't recall which way it moves as the dwell angle changes) will affect the timing. So, do the points first and then check the base timing, adjusting as necessary.
One other thing that might affect point life is crankcase ventilation. With time, it can be possible for the crankcase vapors to get into the distributor, as there are no internal seals to keep them out. That could mean evaporating condensate from the crankcase too, in the case of engines that don't run that much at a time. Usually, that's not a real problem for vehicles that get up to operating temperature and stay there for a good while or in climates that don't see sudden temperature swings.
We all know that points used to last something like 12,000-20,000 miles when our cars were new. With proper care and lube when installed, I would suspect similar performance might be available now, but as the previously new distributors have worn, it could be those wear issues that are causing the problems, whether it be the worn bushings, breaker cam, or combinations thereof.
As for spark knock in one engine and not in another, could be several issues there, not to exclude deposits and such or production tolerances from engine to engine. Factor in the cylinder to cylinder variations from the cam lobe wear in the distributor and it just might be one of those tolerance "build stack" situations. Might also be that one of the advance weight springs has broken too (they are located below the breaker plate, but checking the timing above idle might be an indicator that something has happened).
Sometimes, with older engines, it's necessary to vary the factory settings from what the originally specified adjustments might be. Automatic choke thermostat coils is one and ignition timing might be another, just tweaking things until they work right for the particular engine and vehicle. As I recall from earlier calculations back when gasoline was gasoline, on a Chrysler B/RB V-8, about 2 degrees of initial timing might result in 1 Research Octane number less in what the engine would require. Plus finding the original SAE transaction (paper) that Chrysler engineers presented in 1957 on the new wedge replacement engine for the previous Hemi, the 413, and finding that it was spec'd for 97 Research Octane rating fuel. In modern times, that equates to about 92-93 Posted Octane unleaded fuel (from calculations I made back in the '72 time frame when Posted Octane was being phased in). Octane requirement is also reduced with altitude too, probably due
to the lessened cylinder pressure in the thinner air "up there".
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