As far as building upper back strength with the SSB, I've found doing a Westside style box squat builds my upper back as well as deadlifts.
Good mornings even more so.
You can even just sit down on a bench with it on your back with no to little weight on it and do upper back extensions supersetted with shrugs.
I just looked up husafel stone. I know very little about strongman so take what I've got to say with a hefty chunk of salt, but it really looks like zercher or front squats would be more relevant. Especially zercher squats since the center of gravity looks most similar.