There should be now problem moving the waist level finder between models. I myself have a waist level finder that came off my camera when I purchased the camera, and that waist level finder to this day sits in my camera bag unused, ever. I use a 45 degree PME prism which has a built in light meter.
Practically everything made for a Hasselblad film camera is interchangeable, with a few exceptions. One example, the Hassy advance knob light meter can not be mounted on my 2000FCM. I have the chimney finder, excellent for viewing slides, a 45 degree finder, used mostly when using very long lenses, and the waist level finder, which I use most often, because I find it the most comfortable to use. Everybody works differently.