Looks like Boeing took a shortcut to put in the third radalt for triplex autoland. The outboard ones would be for the third radalt.
As holdover from the 737-3/4/5 series, the ones on the centerline are probably lined up T R R T or vice versa. That would make the third set ok for R T alignment (or v-v).
The triplex alignment on a 757 uses the same wedges for the left and right radalts as you show here, while the center radalt is on the centerline. I would post a pic, but it's not on a website, and I don't see how to load it here off my HDD.
GB