Google Maps streetview can show you highway and its shoulders in full detail. My guess is that the shoulder width will vary from state to state.
In ND I'm seeing 18" or so of pavement outside the 'fog line' (white line on the right side of the lane), with gently sloping grass beyond that. In SD that sloping surface is gravel for about 3'. Manitoba looked the same, except I didn't see a fog line.
Up north at least, traffic is light enough (and sight distances long) that it would be ok to stop in the traffic lane itself to do something like change a tire. Or at least stop long enough to look at the shoulder on foot.
For something less urgent, I'd wait for the next farm cross road.
In Nebraska the paved shoulders are wider. From satellite view they appear almost lane width.
Overall I don't think driving US83 will be that different from driving a numbered 2 lane highway in Saskatchewan (e.g. 39 or 47).