I don't think a slide in style 9x12 rollback will work with an Ideal. I don't have a 9x12 slide in back to test this, but I do have 9x12 Rada rollbacks for Zeiss Ideal and Perka cameras, also a 6x9 slide in Rada rollback.
I should point out, I've not seen a Rollex rollback, but my best guess is that it wouldn't work, unless you were fortunate enough to find one made specifically for an Ideal. The simplest way of getting a rollback that fits an Ideal is to buy one with the camera. I think I remember reading a few posts from people who bought rollbacks only to find that they didn't fit their particular camera.