Glass and Mirrors - Hanging a mirror on Concrete block wall

I want to hang a 72" x 42" borderless mirror in my basement. The walls are painted concrete block. I will probably use those clips that secure the mirror to the wall around it's perimeter but I am not sure what to use to secure the clips into the block wall or how many to use. Any suggestions?

Concrete block walls are generally not perfectly flat and could be damp. Secure a piece of 1/4" plywood at the top and bottom cut to the width of the mirror. Now you can screw a 3/4" J molding at the top and a 3/8" J molding at the bottom. The correct placement is important since you will lift the mirror into top molding, clear the bottom molding by 1/8" and drop it into the bottom J molding. Use flat head screws and plastic anchors for the plywood & the J moldings.

I would drill and carefully clean out holes in the blocks then epoxy in anchors, the mirror is heavy and plastic anchors probably will not hold over time.
remember Murphy was an optimist

Ugh, this is getting more complex than I wanted it to. I also want to be able to take the mirror down and fill the holes if needed. You don't think using concrete screws would be enough to hold the mirror clips? Or plastic anchors?