So since I'm on vacation I thought I'd give it a shot. Unfortunately I don't have a shoebox, but I do have an animation light table. So using paper, glue, paint, tape and a piece of cardboard I made my own negative holder.
And here it is zoomed in.
And using the filters and functions of the phone's picture editor I was able to rotate, invert, crop and adjust the negative. And here is the result.
I'm having some issues with color negatives. I think it's because they're a bit old. They have a blue haze over them that I can't seem to get rid of. I tried adjusting the levels in Photoshop but they're still not coming out right. I'll keep trying until I figure it out.