Dang-First thing Id do is cut up some better blockage for the rear with board across incase box shifts side to side.-Second is I might screw a post to beam. It appears the strap went around face of box then under to floor anchor. I cant see this working with the weight, using strap as a lever-using force of strap straightening out instead of pulling. At least how I'm seeing, once it reaches a point force on strap (or anchor) increases, movement of box decreases- quickly taking everything to limit .
With what you have- I'd wrap the strap around front of box as you had done but continue to wrap the box (don't anchor the strap to floor or back to the strap itself). , should wrap the box. You may need another strap to keep the lifting strap from slipping. All force would be applied at front corner, once it reaches a point I would assume the bottom front may slide outward righting itself. Thats a lot of weight. But hopefully youve got it up by the time responces read.
Only other thing I can think of is addtional strap wound in opposite directon pulling toward wall simutaneoulsy-but Im unsure if I want that load on studs-all else could weld on some lifting lugs. Due to value of box ins 'might' help, DA or not still an accident.
Mark