Is the K4 part of Kryptos a Rasterschlüssel cipher?
Not alone anyways. Rasterschlüssel was a German Transposition cipher that depended heavily on pre-fab grids that the users would all have the same copy of to use for enciphering/deciphering. Imagine a blank crossword template:
Ye olde cipher clerk would take the plaintext and start filling in the white spaces. The top would have numbers on the columns and they would reel off the newly transposed letters in a staggered transposition.
Possible as a portion of K4 but is not enough to give the muted letter frequency seen in the K4 ciphertext.
We would face the same difficulty as Bletchley Park however in that without the template, it would be nearly impossible to even guess at how to reverse it.
Maybe someone will see a use for it but this isn’t anything I can work with.