Just an update on this:
I humidified the guitar thoroughly for a few days prior to gluing and cleating. As a result the cracks closed almost completely and virtually disappeared.
I purchased hide glue and a glue pot, prepared it but couldn't get any in the cracks from atop (no enough space to use the "suction cup" method, the brace was kinda close to flex the edges and the crack was basically shut). So I warmed up the area with a halogen lamp and applied hide glue from underneath => the heat and water from glue opened up the cracks and swelled the top a little
So I've quickly cut two cleats and applied them then clamped everything with a small flat wood bar on top to level it and prevent swelling. Left it alone for 24 hours.
A few days later I've applied the second pair of cleats which was pretty challenging from a clamping perspective.
And here is the work completed:
