Seems the Bronica RF645 was introduced just as the market for such cameras was declining, and so production numbers were somewhat limited. But IMO it was the most advanced technically.
Early-on, there was a 135mm lens offered with matching framelines in the viewfinder. Due to manufacturing tolerances, some body/135 lens sets had trouble with accurate focus. The UK distributor on their own set up a service for matching a customer's 135mm lens with their RF645 body, a good solution.
But Bronica had been bought by Tamron as I recall, and the corporate decision was to recall all RF645 bodies and 135mm lenses. The 135mm lenses were replaced with 100mm lenses, and the cameras were refitted with 100mm framelines. (Jim and I appear to have posted this tidbit about the same time!) The shorter focal length was better able to withstand existing manufacturing tolerances, it appears.
Not all cameras and lenses were returned for the recall campaign, so some of the originals are still out there in the used market. It may still be possible to get the viewfinder frameline mask changed...
Cameras manufactured after this focal length change have serial numbers starting with 11, while the original body serials began with 00. Of course bodies with 00 serial numbers are likely to have been refitted in recall, but not all.
BTW, there is no frameline in the viewfinder for the wide 45mm lens. Instead, this lens comes with an external finder. I found that the whole VF window was a reasonable approximation of the field of view, however. I've wondered... had the camera been originally designed for 100mm at the long end, if the VF magnification were a little lower this might have allowed proper parallax-corrected built-in 45mm framelines.
I bought a new RF645 in 2003 under a rebate program, with all three lenses (45, 65, 100). A much nicer camera all-round than my previous Fuji GS645S. And it reminded me a lot of my well-loved Minolta CLE. These are both all-time favorites.
Obviously I can't suggest that you will like the RF645 as much as I, but it's a wonderful camera. So much that I bought a second one used w/135mm framelines hoping to encounter the matching lens at some point... never did.