Well, this counts as a "new" acquisition for me ... I converted my Mamiya 55/1.4 to a M42 fit the will fit on my K-1 and others. As you may know, Mamiya M42 lenses will not easily mount on K-mount without removing the flange at the base on the lens plus the aperture index pin.
So, I dissembled the base, cover it with electrical tape to protect the threads, etc. and went after it with a file. Here are the preliminary results and it's just a hair shy of infinity which is no big deal for me ... not planning to use this lens for landscape, but maybe later I will modify again.