The 67 body is only required to be set at 1/8 sec on the dial when a leaf shutter mode is engaged. At any other time its selection is arbitrary, e.g. if the aperture is set as desired and the meter needle is brought up to mid-line if the shutter speed is set to 1/8.
All Pentax 67 bodies have the intended design function of not firing the shutter unless there is a film loaded in the chamber.
If the camera can be dry fired no film loaded, the safety pawl that governs the shutter release and wind-on is obviously broken, or it has been tampered with. The only way of overriding the function normally is to use a special tool that is inserted underneath the film advance lever that 'tricks' the safety catch into the function of releasing the shutter without loading film (useful for checking). This tool is supplied with the camera as OEM.
From that last part it can be assumed the shutter speeds are accurate even if you are resorting to guessing with the "in-between" stops. I'm wondering if the dial at some stage in history has been forced beyond its limit (continued around where it usually does not). There is a pawl mechanism in the shutter speed dial that governs the click stops an "in between" setting will render an incorrect exposure, obviously (as published by Pentax). Rapid and forceful rotation of the dial is known to strip the pawl stop out very similar to the terribly onerous problem with Canon's EOS 5 mode dial where the click-stops are stripped out from the flimsy plastic pawl that selects the mode (the problem often recurs because of an inherent weakness in the dial's design).