Having worked my way up the walls it was time for the final major interior improvement in the cargo area: the ceiling headliner.
2.5" long, 5/8" hex, 1/4-20 threaded standoffs are attached to existing holes in the roof ribs, 4 per rib for a total of 20. The inboard standoffs are attached with shoulder bolts as there is access adjacent to each mounting hole. The outboard standoffs are attached with pre-bulbed riv-nuts and short lengths of all-thread to which thread-locker adhesive is applied to one end of each. Additionally, the inboard standoffs are cross drilled to accommodate a rope which is used temporarily to support the insulation during installation of the panels.
The headliner is cut from ~1/4" thick polypropylene hex-cell panels that I purchased from Penn-Elcom.
These are the "M865004-M865010 Flight Panel", which is a very nice material, superior to what Ford uses for the wall liners. It comes in 7'-7" x 5'-2" sheets, which allows the ceiling to be covered by only two sheets with little waste.
The headliner meets the walls ~4" below the roof seam. At this height the ceiling is of constant width for most of its length but tapers ~1.5" at the front and ~.75" at the rear, so some fitting is required. The headliner is scribed around the forward foam blocks and its forward edge rests on the partition.
R-13 glass fiber insulation was temporarily supported in the middle by the rope threaded through the inboard standoffs and at the edges by small pieces of tape. The rope was removed after the panels were placed and the tape should let go in due course allowing the insulation to "get comfortable".
I was unable to source any suitable divider molding for the joint between the panels, so the joint consists of two pieces of extruded aluminum carpet molding clamped together by 10-32 screws and riv-nuts.
4 LED puck lights from SuperBrightLED.com are installed in the headliner. The two original cargo area lights on the aft bulkhead are retained with the festoon lamps replaced by LED modules.
Now I need to drive a few washboard roads and see how it all holds together.