What I have done when needing a focusing mount is to find junk metal 35mm faster normal lenses (with your camera mount) and strip them down... Harvest the optics for experimental lenses or loupes, remove iris assy and anything else in the way...

Front group usually has a front shroud with a set screw or 3, and will unscrew... Group has a set screw, then it will unscrew... Rear group will unscrew, but maybe some thread lok acetone will loosen... F ring might have a set screw on bottom, then all iris stuff out... Might have light baffle stuff, so remove...

But first see how high the (lens) mount is and if the new lens might slide into it (hope you can focus to infinity)... Many o-scope lenses are 75mm (3"), so that should be around the extension lens to "film" plane...

But if there's a big fat rear element on your new lens/shutter, it won't fit into the mount... And you will have to jury rig a way to hold lens to mount, but rubber or plumbing stuff might do the trick...

Try not to damage any of the mount ' s threads, as you might later like the lens enough to have a machinist make permanent metal parts for long term use...

Have fun!!!

Steve K