Had a look at their site, they are pretty good!
So far looks like I might be ok.
Below are my calculations... please correct me if I'm wrong:
Pentax 67 lens focal length: 84.9mm
QSI583wsg with T-mount back focus: 50.17mm
Adjustment for filter (Astronomik 1mm thick): -0.33mm
Net back focus for QSI = 50.17 - 0.33 = 49.84mm
Adapter thickness = 84.9 - 49.84 = 35.06mm
Estimated cost from Precise Parts: $330 + $30 shipping.. yikes
Victor.