To alan_b when you mention some pieces to allow shifting of the Contax 645 glass, are you referring to a Mirex adapter? Or is there some other part out there to do the job?
I'm making mounts to use my Arca 4x5 as a test rig first. Next is modifying a Kipon shift adapter to have a C645 mount as a semi-permanent solution until I settle on a view camera platform. (The Kipon is a copy of the Mirex - since I'm modifying it anyway, I can tune up any tolerance issues.)
Really, going with Pentax lenses would be the rational thing to do - shift adapters and Actus lens boards already exist. I guess this is just an excuse to tinker!