Hey my fellow Pentaxians!
I've been reading this thread and been shocked about how you butcher your old cameras to get a split image screen for your loved MZ-S. Though I am a new member, not quite new to the brand, camera repair and mechanics. So just help you out here I can tell the secret (as a user and owner of two (2) MZ-S bodies) that you do not need hardcore actions for a manoeuvre like this. The most apparent solution is:
GET A FOCUSING SCREEN OF AN MX
It needs to be adjusted to the MZ-S, but takes only about 2 minutes as it is practically the same size as the MZ-S's screen. Kudos Pentax!!!
Pentax MX screen is about 0.3-0.5mm bigger both in lenght and width, and the small pin on its front is placed by about 0.8mm towards the center. So the extra needs to be removed from the mentioned places and there you go. The adjustment has no serious effect on the screens' usability on an MX if it comes to that one day again.
As soon as I have some time I'll post a detailed, pictured thread how to do this. Till then feel free to ask any questions about this.