In doing this on my ‘46, the trim pieces needed to be screwed into place as the liner was installed. Really tricky to do working solo, but I was able to get it done. I recall using a couple of thin, bendable and padded sticks to compress and hold the liner in place against the roof on one end, while using a couple of the Irwin-type squeeze clamps to hold it in place and help align the headliner in place while securing it with the trim and clutch head screws on the opposite end. I don’t recall with certainty, but there were likely magic four letter word incantations uttered as well.🤫
As for orientation of the center rib molding the concave side fits as shown in the attached photo.
