Originally posted by abruzzi thanks. Since you seem to be pretty knowledgeable about the 67 models let me ask a quick followup--is there a functional benefit of a 67 over a 6x7? I get that the 6x7 is older and therefore has potentially more wear and tear, and the early 6x7s won't have the mirror lockup. I've found some past posts implying a the 67 had a brighter viewfinder, but that doesn't seem well sourced so its hard to know whether to believe. Other than that they seem to be identical, and the meaningful changes all came with the 67ii. If I get one, and I am leaning that way, I will almost certainly try to find a 67, and while I can't spend a lot, I'm definitely the sort that is willing to pay a premium based on condition.
Either/both cameras operate the same. The changes were in engineering/parts, lubricants, correction of known potential faults and something to do with the resistor pad underneath the shutter speed dial. To a new user, looks can be confusing, because the older/early Asahi Pentax prisms or chimney finders also fit the newer generation Pentax 67 bodies. Likewise, older 6x7 bodies are often seen repairs with 67 top plates or other parts! The sheer diversity of changes can make determination of what body is what a challenge. Moreso an older body and not knowing if or how it was repaired (something about the shutter blind tape deteriorating in the original Asahi Pentax 6x7 bodies was fixed too.)
Fora commentary the speaks of a bright viewfinder requires careful judgement. Some may have been fitted with Beattie IntenScreen focusing screens (and worse, not even re-calibrated to achieve correct focus) to provide a brighter image, but really, any competent, skilled photographer can easily work with the native Pentax 67 focusing screens (they look course/dark with slow lenses, and at the opposite end with fast f2.4/f2.8 lenses, bright and easy to focus), even in challenging low light conditions, and additional focusing aids are available to further assist. Don't always poke an accusing finger at a camera's perceived failings!
Mirror lock-up is very, very usefulu for separating the inertial whack of the shutter and mirror in tripod-based work, lessening (read: eliminating, when done properly) any chance of blur. Another, much rarer feature is a multiexposure facility that was often factory fitted or the change made upon request and at cost: press the shutter, flip the ME tab to M, wind on (this is a "blind action", no film actually moves in this process), then do the second and subsequent exposures. When finished, flip the ME tab away from the M and you're done. When my Pentax 67 came along I was puzzled by this little tab until I was told what its function was. Since then, I'm pretty much carried away "layering" shots for unique effects.
Lots of people use the Pentax 67II, but it didn't appeal to me. It' the all electronic, updated wunderkind with the addition of multimodal metering, AEL and other little niceties and won't shirk any any of the Pentax 67 lenses on offer. The 67s are primitive by comparison ("steampunk" is my term!), but they are excellent, reliable workhorses that get the job done, relying more on the photographer's skill rather than the camera's decision making and winding on. Oh, how awful: I cringe when my EOS 1N blasts through 36 exposures in 3 seconds because I am so accustomed to the tweak-whirl-slap winding process of the P67. But every kid needs his thrills...