Ahhh, a walk behind tractor.
I was thinking of a larger tractor.
Russian? You might have troubles finding specifics about that machine in the USA.
Following some of the links, this either is the
manufacturer or a vendor of similar diggers.
I found this page showing a
homebuilt digger. It has a 3pt version shown at the bottom of the page, along with parts diagrams for that one. Perhaps you can find the parts diagrams for your target machine.
The "shaker" undoubtedly helps with the separation of the dirt from the potatoes, as well as aiding with the cutting (probably vital for a walk behind tractor). You would need to design a frame that doesn't move, and the cutting head and separator that does.
Are these machines patented? A lot of info is available on the patent pages.
However, keep in mind that ultimately you will be making your own machine. You don't necessarily want to copy exactly a commercial version. but take some of the ideas from several ones you see.
These all have an adjustable depth.
Width may be dependent on how you plant your potato hills, as well as the design of your tractor/tiller.