Simplest solution for hanging 50lb frame with welded hooks

I have a 50lb mirror I'd like to hang. It has an iron frame with two hangers welded onto the curved top edge on the back. Here's a close-up of one of them:

enter image description here

The hangers are about 17" apart on center, and the keyhole cutouts are 3/4" wide. The wall is standard drywall, and there happens to be a stud dead-center where I'd like to hang it.

What are the simplest and safest options here? Considerations:

  1. I haven't checked yet but there's no guarantee that the brackets are 100% level, so the solution needs to be able to account for that.
  2. I'd like for the mirror to hang as flush to the wall as possible, minimizing lean-out and gap.
  3. I'm pretty conservative re: hanging weight and would strongly prefer using the stud for support, although I can be convinced otherwise. I saw this (Hillman no-stud hanger) mentioned in another answer and perhaps two of those could work if the result hangs fairly close to the wall, although point #1 could make this very challenging.
  4. Preference is for a minimum of "construction": cutting wood, etc. This technique (spanning plywood) seems to be a good solution, and I can make it happen, but if there's something simpler that is as safe I'd be interested.

My experience with hanging anything close to this heavy is to just use a z-bar, but I don't have that option with this frame.