[mr48chev]

"Octane adjustment" = resetting the timing to get along with some of the crappy gas that was around then. Not as bad as some you see these days but in the 50's and early 60's if you didn't go to a decent volume name brand station like Chevron, Texaco, Shell or Union 76 and stopped at some hole in the wall one pump station you stood a chance of getting gas that barely could be called gas and might be doctored with coal oil or some other cheap fuel to boost the owner's profit level. Or the guys who lived down on the border who drove over into Mexico to fill up at the time.

Now days it is more in the way of a way to fine tune the timing down to the N'th degree while on that distributor. If you have an adjustable timing light it is easy to have the ball on the flywheel line up with the pointer and then dial in the exact timing you want with that setup.