measure the distance between the concrete and the upper 2/3 drywall. Then with that measurement deduct the width of the furring strips and then use that figure as the width of the drywall to use.
furring strips or nailing boards will be attached with liq nails for concrete and concrete anchors. Then the nailing boards spaced about 12 OC will be used to screw the drywall into. Use the right lenght drywall screws because if too long the screw will force the nailing boards away from the wall.