How to smooth out vertical concrete
Barring some of the other issues, like what is holding the hollow block up over the window, and are the bolts through the double ledger going into the core of the hollow block or....I usually smooth out the rough spots with a grinder so all side are flat and reasonably plumb and level. It really needs to be flat. Then I set in place a pressure treated 2X8 cut to go across the bottom and one for the top. For the sides, I cut each side really snug so they need to be driven in with a beater block to help keep from splitting the wood and a hammer. Before hand, most pieces need to be dry fit to make sure they set well to the surfaces, since polyurethane construction adhesive will be smeared, shot, gunned, squeezed over the surfaces that will touch the wood before it is set in its final, permanent position.
Hold the PT material flush to the outside wall, since the inside can be filled with ripped material during the finishing stage. Before the window is set I would use a liquid applied waterproofing membrane to seal the outside from water infiltration. Then set the window, then seal that too. Then the outside can be trimmed out with PVC trim to finish it off, covering all the waterproofing that was applied....neatly.