Floating granite shelf/bar install question

steve65

Need some advice on this install. I'm installing a floating bar on the back patio right below a window. It is a block house with the exception of this particular wall (of course, right?). The piece I'm putting up is 1.25" thick x 12" wide x 74'' long and I have 4 heavy duty brackets. They are specifically made for granite so I have no concerns with the brackets. They are gusseted L brackets made from 1/4" thick steel.
The concern/ question is the wall itself....the studs are not in ideal locations. I can hit 2 vertical studs with the brackets, but not all 4. Although I can hit the bottom sill plate of the window with the top holes of all four brackets. This would leave the bottom holes of 2 of the brackets with no stud to attach to. The only reason I'm even considering this option is that the stucco on this wall is about 1" thick (and I would assume some sort of plywood behind it) so I'm thinking I might be able to get away with it.
Any opinions on this one?