[Lynn]

For completeness: for the proper depth at the top, the proper height and to help secure the fixture I added the small block you see in the picture below. (You may have noticed in the first picture that the bottom dowels appear to be below recess plug; and they are.) I left the top of the recess open, which eased mounting the latch tremendously. Since it was open topped, I also wanted the back wall to be high enough so that the opening was not visible even when the clip was in the opened position. The thin piece extending from the block (at the bottom in the pic) was for clearance for the sill mounted part of the latch to extend from behind and under the recess.