Attaching a digital back to a 6x7 body is pretty much pointless, since even a 50mm lens won't be really wide angle with even the biggest digital sensors you can buy at the moment. The biggest advantage of the Pro IID is the fact, that it's most likely newer and as a result in better shape than a Pro or Pro II. One shouldn't forget that bot RB and RZ were serious professional cameras which saw heavy use. If you go to a used camera store, you'll be amazed how scratched and dinged some of this equipment is. My used Pro IID was marginally more expensive than comparable Pro II offerings and it looks and works like a brand new camera.