Thank you for your help and guidance.
Since making my first post, I have managed to get ahold of a replacement slide stop.
I have also realized that I am an idiot, and that the rear sight is indeed fully adjustable, and not only sideways.
We have also managed to find an old range bag that belonged to my FIL, which contained a different set of sights that don't seem to fit.
The oval is marked "89", which helps identifying the age.
It was CZ Europe I contaced, and they apparently won't release any information except when it is a matter of an official police inquiry.
Here are some photos I took, the last one showing the pistol with the right side lever removed:
(Apologies for the huge pictures, I can't figure out how to make the photos smaller in resolution... Imgur album here: https://imgur.com/a/amxhgSm)Thank you for the help! I like to consider myself savvy with computers, but it has been a long while since last I dabbled with HTML and messageboards...
After having looked around a bit in the forums, it seems like there have been many types of 75s and 85s throughout the years, so I still feel a bit lost.