Yes, the plastic pin is easy to push in (although it won't stay in), and I can now see that it appears to be pushed into the switch by hydraulic pressure -- it's when the pressure drops that the pin drops down.

As for the ATE front calipers, they appear to be assembled in exactly the same way as the original front calipers I removed from the car. And, because the top bleed screws on each half of each caliper are canted toward the front of the car (as opposed to being in a straight vertical position), it seems to me that it would be impossible to have a misassembled ATE front caliper that was not readily apparent on a visual inspection (since an incorrectly assembled caliper would have one or more bleed screws canted or actually pointing toward the rear of the car).

I do have to plug up the hole in the junction block into which the switch screws in order to bleed the brakes, right?

Thanks for all of the help!