Early Dart Headliner Install Question

I vaguely remember that the seam going down the sail panel had a continuous channel. I didn't cut it away, just cut a slot for the bow to run thru. Re post 14, I recall reading someone else mention a "nail", but don't recall that in my Dart GT 2 DR Htdp "as found" though a long time since I stripped it. I did find 2 "push-pins", like the door panel clips but with a pretty button top. I suspect those secured the rear "package tray", though I didn't use them. I cut ABS panel for that.