I think they changed to the pucks around 1974. I don't know exactly why, but Fords were using the same drive about that time frame. In fact, the pucks are available, just have to type "Ford" in the search on eBay. Exact same.... Possibly the same vendor making them.
The worm gear adjustment is there because by their nature, the pinion for will want to push or pull as it turns the driven gear. The reason they use a worm gear is because the pinion can't be turned by the driven gear. So a window goes up and the weight doesn't push it back because the worm gear won't let it. That's a really crappy explanation so here's something better.
Worm Gears Explained
Worm drive - Wikipedia
