This is completely pointless info, because:
1. I seriously doubt anyone has a stock standard engine.
2. You can NOT get vintage gas.

Back in the day, the fat spring was used to DELAY full timing at peak torque. Today, you can get fuel much better than 1960's fuel, so you can bend that fat spring tab in & gain midrange torque/power & economy.

The thin spring you can loosen until it pings, then tighten it up a little for more improvement.

There are still special cases: I have a K-Jet B20E with a race head & 11.7:1 compression. It needs & uses 10°@idle & 20°TOTAL. It was my old race engine with Twin 48DHLA's, etc. with monster cam. When it was my race engine it ran a locked distributor. 27° with the average leaded fuel I could get, 34° with some Toluene mixed in for track useage.

Vintage Cams: No one should be driving around with A, B or C cams when the vastly superior K has been around for decades. For example, KGT sells a K grind for B30A's.