The holes are 76mm apart using the existing #8-32 screws, where both seem to be somewhat of a standard after checking online hardware stores.
There are files for: horizontal handles with the hook on the left or right side, vertical handles with the hook at the upper or lower position, and a regular handle for horiz. or vert. I've been using them for approx. 2 months and they remain secure. I used PETG
I need to acknowledge “SmilingImpact” for the make of his/her 8-32 Bolt & Nut, https://www.printables.com/model/226487-8-32-bolt-and-nut, to help figure out the internal threads, which was driving me nuts. Thanks SI..
The author hasn't provided the model origin yet.