if your interests are to photograph with the use of a tripod I beleive that there is a device available for the Mamiya TLR called a Paramender. This device allows one to focus conventionally with the top lens and then to move the taking lens into the position of the viewing lens and to remove parralax fron the photo taking process. It does not allow for depth of field preview.

I have never used one of the Mamiya TLRs. I do own though an RZ67. My main disappointment with the RZ67 is the PITA in using the depth of field scales. The camera has very nice depth of field preview but when the light is of very low contrast I would welcome a more user friendly depth of field scale.

I am to unfamilar with the Mamiya press cameras to talk with authority about them but I believe that they have a ground glass back available. If that is correct and since you like rangefinder cameras this could be an option worthy of investigation. Of course you could also look at the Koni-Omega cameras. I do not believe that they offer groundglass viewing but I could easily be wrong. The Linhof Technika roll film cameras do offer both rangefinder as well as groundglass viewing but you may be getting to closer to Hasselblad prices. They are without about, for a person that uses a tripod, the most flexible of the lot offering both lens movements and a back adjustment. The Horseman press is also similarly flexible.

Good luck with your search.