Just out of curiousity, do the Autolites center electrodes extend as far into the chamber as the Champions do? If not, that could effectively retard the spark a few crank degrees in itself, even if what it's showing on the damper is correct.
I haven't checked the Autolites, but if they have a wider heat range than the Champions, they could effectively be a little "cooler" range plug. But most of the older 10.0 compression ratio B/RB engines could have gone as "cold" as a J9Y for the higher performance camshaft motors in the earlier 1960s. Compared to the J14Y in the 9.2 compression ratio 2bbl motors, that's a pretty cold plug, but might be necessary for extended WOT running (i.e., police pursuits).
Several other construction variable might include copper cores and similar heat dissipation items, but the length the center electrode extends into the chamber could be significant by itself. In the earlier times of using Champion plugs, I never had any problems with them, but your experiences might be different.
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