I have an RB but I can't say whether the 645 prism fits. If I had to guess I'd say no, the 645 should be a smaller system. You can get a prism finder for the RB. The lenses definitely won't fit. I think.
Edit; I'm gonna say no and no. Even some of the later KL lenses won't fit the earlier RB bodies cos they changed the diameter of the mount/rear flange, so if you're thinking of a body, better to get the later Pro-S (or the Pro at least). The earliest lenses are single coated (non C), the next C lenses are multi-coated and better, and the KL lenses are excellent.
It's often a good idea to buy this type of system as a complete kit, as it's getting more and more difficult to come by second hand equipment. Usually the more gear being sold at once, the better the deal.
And I have a question. I have a heap of old slide film that's years(?) past its use by (but probably still OK). Does anyone have any ideas for something interesting to do with it? I was thinking of heating it up a bit to make the colours change. Perhaps just cross process it. I have 9 rolls of Provia 100F and 1 roll of 400F. Anyone know of any cross-processing methods for Provia? Or something else?
I made this 50x15 print for my parents to hang above their bed. I built the frame myself and wrapped the picture around it. I know it's all wrinkly and the framing is terrible, but it looks a lot better in real life.
I think most of the changes were requests from clients, they start off as photographs but end up as adverts. That tool is extremely cool, incredibly extremely cool, especially for people with cloning special needs like me.