Did you know that DHW-Fototechnik makes a sliding back for their X-Act2 Cameras?
Here's a picture of what it looks like and the different components that go into it. The sliding back takes a viewfinder adapter piece and a digital back adapter insert plate. Shown are the Rolleiflex 6000 series viewfinder adapter piece and the Hy6 adapter piece. The DHW sliding back adapter with the Hy6 insert fitted gets the sensor about 6mm closer to the lens than the Kapture Group sliding adapter which means a lot for work with wide lenses.