I wrote some of this on another thread. Maybe it will help, and I believe it's accurate, but the dealers can correct me if I'm wrong on something:
Regarding the RZII non-D:
- LEAF digital backs: Leaf makes 4 adapters (with cable) for Mamiya AFD-mount backs, H-mount backs, V-mount backs, and AFi-mount backs.
- With Phase One backs, you can use an adapter and cables that will accept a Hasselblad V-mount back.
- Sinar backs have adapter plates.
- Hasselblad CF backs have adapter plates.
Regarding the RZIID:
The RZIID can do everything that the RZII non-D can do above, with the added advantage of supporting an electronic adapter plate made by Mamiya that allows ANY Mamiya AFD-mount back, (NOT just ZD backs!) to be used with electronic communication, and no cables, like you would on the 645AFD.