If visible supports look good then thoseDo you want it to look like it's floating (hidden supports) or do you want visible supports?
If it were me, i would use threaded bar and resin.
It's heavy, I'll put two resins bars in. Never put a resin bar in before. How deep into brick work? How high above fire?Drill the wall, drill the edge of the timber to match the holes in the wall, then resin both in the wall and the timber holes, for the threaded bar.
I would support it on a temporary frame whilst it dries, or you end up having a droopy resultIt's heavy, I'll put two resins bars in. Never put a resin bar in before. How deep into brick work? How high above fire?