OLC is short for Onelifecrisis. The person that made the mod goes by that handle here on the forum.
I am not sure anymore about compatibility with different flavours/mods of Sh3. He used to have different versions for each flavour. But at some point he managed to make a version independant release. He made several mods that contain these periscope changes:
OLC Gui 1.2.7 (modified scope optics and completely overhauled interface) (uploaded on my filefront page in a subfolder)
OLC Ubermod 2.43 (Environment changes plus single-magnification attackcope in OLCGui fashion) (uploaded on my filefront page in a subfolder)
OLC Gold (OLC environment2 plus OLC Gui for GWX 3 only) (not uploaded to my filefront page)
Here is a link for the OLC Gold so you can get an idea of what it is:
http://www.subsim.com/radioroom/showthread.php?t=147667
The rangemeasurement is still a sort of stadimeter. Except the moving line is gone and you need to asses which mark is near the mastheight. The sliding scales then calculate the actual range. Following that the same scales can be used to calculate the AOB based on the appearant width. I think pretty similar like you seem to do using the mk1 eyeball. But this is more like the actual attackscope used by the germans.