Will estimate those pieces are about 20 to 40 lbs.
Just two d-rings, one on each side. Easily handle 40 lbs. I usually place them 6 inches above horizontal center which tends to keep the piece snugged up to the wall.
Of course you can always use cleats as discussed elsewhere. But one advantage of the two-point d-rings is that the wall doesn't have to be perfectly flat. Another advantage is simplicity. It's how most museums hang their medium large pieces.
I like d-rings with flat oval tops, like
these. It allows for left-right expansion and contraction of the piece, although there won't be much with Masonite. Also makes nail positioning a little less critical. Pointy-topped d-rings need closer measuring tolerances, and generally make life too hard.
Have many pieces mounted to Masonite from the 70's, still in good shape. Would use it in preference to Gator if:
1. it didn't weigh so much.
2. it could be cut well without a table saw and without making sawdust.
3. my back was in better shape.
edit. Oh yeah, safety. Put the d-rings about 1 inch in from the sides, and twist a safety wire loop between the nail/screw and the d-ring. Easy to do if somebody else is taking the weight off that side of the piece and the ring itself is temporarily flopped 90 degrees to the wall. Ballistic kid proof if done properly.
