Sanders, my guess is that the Rittreck holders won't fit. I have a set of the Rittreck holders to match my Rittreck camera with "yatsugiri" adapter back; they're too long to fit my older American WP cameras (Eastman, Century, Gundlach Criterion). But since they're on the way, soon enough you'll be able to check for yourself.

A bit of trivia: the Rittreck yatsugiri holders actually aren't "Wista" holders - they were made by Tachihara, as was the yatsugiri adapter back for the Rittreck.