I personally think you should move your sights to at least 1975 or 1985 or even 1995 adyour cut- off point for medium format cameras to consider. There were a few somewhat uncommon cameras made in the 1960s and 1970s which were really pretty neat.I think that in terms of reliability perhaps you should look at twin lens reflex models such as the above mentioned Rolleiflex and Rolleicord models, as well as the Mamiyaflex C220 and their C330 twin lens reflex models, as well as the Mamiya Universal Press ( a 6x9 cm rangefinder) and the fairly rare Linhof 70, which is a beautiful but very rare camera.
One thing to look at is the film. 120 film is easy to get still, but 220 film has become pretty hard to get, and limited. 120 film cameras are divided into three types: the first type uses a hinged back ,in which the film must be loaded one roll at a time. The other type uses removable backs with an insert,which allows inserts to be pre-loaded and the back swung open,and The insert simply placed inside, then the back closed up. The third type uses a self- contained back which is preloaded as a whole unit; if you have more than one back, then you simply swap out the entire back. If you only have the one back, then it in effect becomes a pretty slow loader.
As you probably realize, the capability of switching out film types or speeds mid-roll used to be one of the big advantages of roll film cameras As opposed to 35mm cameras. I am only aware of a couple of 35mm cameras that used interchangeable backs, and for the most part a35mm camera is a one- roll- at -a- time camera .