If you look at the pictures above there is a hole/slot with a tab sticking up through it. At the opposite end from the tab and barely visible is the edge of the stop. The torx screw threads into the stop and locks it in place. When you loosen the torx screw and slide it back and forth the stop reduces/increases the length of the slot.
The tuning kit spacers stick into the slot and you loosen the torx screw and slide the stop up against the spacer and tighten the screw to lock it inplace. Much easier than messing with a degree wheel or using trial and error. Plus the springs let you dial in the rate. As you reduce the amount of advance in the distributor so you can run more initial you need to go to a stiffer spring to have all the timing in at the same rpm.
