Wrecked wooden lintel and no sill on basement egress window.

I’ve got an old in-swinging emergency exit casement window in my basement, that exits to a light well with a hatch above. The wooden lintel/head jamb thats set into the cement is ruined, the sill is gone, the jambs are rotting away, and I’m ready to do something about it. I’d like to keep the original wood window, but I have no idea what to do about the lintel and sill — especially since the sill sits level with the bottom of the light well (which has an often-cleaned drain, thanks to yours truly). Anyone got a similar setup that can share?