The below comments are what was provided on another forum, and I think much of the information is helpful.
This may help, because I spent a few nights of my youth working on a Sun Machine asking similar questions.
I used to think the 60's era GM supplier just flipped the football over, when welding the distributor shaft together, to select between the "performance" and "non-performance" profile. The football on the right in your photo is the "performance" configuration (compare the shape on the football where the horns on the weights close in on the football at zero advance).
The newer replacement shafts have two different and distinct footballs, a narrow (low-performance) and a wide one (high-performance).
The difference is the wider football shape limits the centrifugal advance, on the zero advance end of the slot under the football. Since the weights move less on the "performance" football, the degrees of centrifugal advance are limited. The rotor on the "performance" distributor also moves off the zero advance position quicker as the rpm increases (the advance weight's leverage point off the football shape is more aggressive with less slack in weight travel before it starts to move the rotor off zero advance).
Regardless of the football, a similar aggressive advance weight movement off the football can be achieved if the distributor tuner brazes both ends of the advance slot and grinds the zero and full advance position in the slot to custom tune the position of the weights on the football profile. You can set the zero advance stop position of the pin in the advance slot right before the weight levers off the football cam, and eliminate the advance dead spot that is common with the low-performance football off-idle. The other end of the advance slot determines the total degrees of advance. braze, grind and set the zero advance position first, and then grind the total advance end of the slot to the desired degrees. Brazing the slot also allows you to eliminate the bushing on the advance pin that rides the slot, one less thing to wear out or come lose at rpm.
I have never brazed on the weights or football to tune the slack in the weights at zero advance, I have only brazed the ends of the slot on the plate below the football. You set the zero and total advance positions with the desired slack at zero advance, and keep the weights off the inside of the rotor at full advance. You can then play with the different springs without having to use too heavy of a spring just to eliminate the slack in the weight movement off-idle (the slack that will provide unstable bumpy idle timing with a radical cam and a lightweight spring). This way you can have the rotor held tight at zero advance (at idle) and then turn with advance almost immediately above the idle rpm, even with a lumpy high-rpm idle cam, and limit the centrifugal advance to keep the total static plus centrifugal to 34-38 degrees (or more when running Alcohol).
A Sun machine is great because the trial & error to test out the braze, grind, and tune of the advance slot does not require installation on the engine. You can also tune the distributor without the Sun Machine, if you have accurate timing marks on the balancer (and lots of patience with a timing light). The Sun machine makes the spring selection and curve plotting work faster and more accurate (buy the machine), but the real advance travel tuning is done with the torch and grinder on the advance slot.
This is probably more than you asked for (more than you need).
