The Ankerstein GK-NS, or Grosse Kaliber - Neue Serie (large caliber - new series), are pretty much the same as our familiar GK-NF, or Grosse Kaliber - Neue Folge (large caliber - new series), except for the large arches have a notch out of the upper corner. Sometimes that makes a difference, though not so much here, where the large arch isn't used.
One small difference: in the boxes, the notches are filled with #19 stones. With those stones in place, the NS arch substitutes nicely for an NF arch; without them the NS arch provides some additional interesting options.
In this church, though, it is only the two extra #19 stones that are used, so if you only have a current Anchor #4 set, you can't build this as shown. I think my handful of readers either have multiple sets or no sets, so not a problem.
Good block play.