3 (or 4, but 3 is sufficient) of this type of anchor (ignore the screw), since you need to hold in drywall with a poorly located stud (these things are typically rated 50 lbs or more each)
3 of this type of hook (an L-Hook), in a size to mate with the anchors. Pad with plastic tubing if you feel the need, or find pre-plastic-coated versions.
Mount two hooks on the wall at the 4 and 8 O'clock positions on an imaginary clock face, hooks pointing in. Mount one hook at the 12 O-clock position, hook pointing up or sideways. Insert plate, turn hook to point down (which is also in).
You do need to accurately position the holes, and you need hooks that are long enough to catch the rim of the plate when it's flat on the wall. Otherwise, go with @Dan D.'s hanger suggestion.