Regent (Passenger) inboard (IB) slat - fitted ribs, updrilled to A-4 rivets, disassembled, cleaned, primed and riveted bottom skin. Fitted top skin with some difficulty as some of the predrilled holes on the ribs didn't line up with the ribs, particularly on the center rib. After removing the reinstalling the top skin several time, I finally got the top skin clecoed. I then updrilled all holes to A-4, disassembled, deburred, cleaned and primed. This part of the right slat is now ready to rivet together.