Swap both the taking lens and the viewing lens.
You can swap just the lens groups. The shutter is the same dimensionally, including distance front to back for lens spacing.
Be prepared to have to do some tweaks for basic shutter board distance off of focusing rails. I don't understand all the issues that cause the shims to change camera to camera. Most likely everything will be fine, but just be aware of this. All in all, there are no significant mechanical differences between a Planar and Xenotar Rolleiflex