A simple search on "carb" and "dimple", turns up everything you've asked about... among them, this entry by
Steve530.
Steve530 wrote on 12/31/69 at 16:00:01:...The needle has, from the top, the spacer, the e-clip, a washer, and the spring.
The lock plate has a dimple which is installed down, toward the spacer. It actually sits on the spacer and hold the lock plate off the washer a bit. I have no idea why. The plate has two holes for the screws and three slots. One is at 2 o'clock, one at 6 o'clock and another at 10 o'clock. The 2 and 10 o'clock slots uncover two holes in the diaphram. Again I have no idea why they are there.
Finally the upper lip of the diaphram has a small tab that goes into a groove in the carb body. I assume that this locates the assembly in the correct position.
Steve