There is another kind of "adjustable" advance, which came on the dual point distributors (the ones with the hex on the nipple). You unscrewed the hex and added or subtracted washers to adjust the advance. I have never seen any documentation on how to do this systematically, or which washer pack came with which engine combo. But at one time I had 6 dual point small block distributors, and different ones had different washer combinations — for example, Commando 273 with or without California Clean Air Package.
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