I went to Home Depot and bought a sheet of Masonite and cut my own. Had the one in the trunk when I bought the car 30 years ago and traced it on a new sheet. Actually made it a little wider since I'm not showing the car for points. The car was 29 years old at the time so I don't know if it was...
Laysons shows both of these pieces with the one similar to Collectors Auto at a fraction of the price. The other piece goes under the trunk lid using the button clips
Collectors Auto Supply shows this piece on Ebay, it's not cheap and freight is expensive because of the length.
Trunk Side Panel Board for 1964-1966 Plymouth Barracuda Hardtop 2-DR Brown Rear
Classic Industries has the same decal for $9.99 and also states for "1966 Sport Fury Air Cleaner Lid." I don't know if I took a photo of the old decal that was on the 273 Commando C.A.P. air cleaner I bought, I'll have to look.
https://www.classicindustries.com/product/md904.html
I've had this for awhile, just haven't put it on the air cleaner yet. Mine has a number written on the back DD 633 and mudsclassicparts.com out of California shows this still in stock for $18.76
I would go to the Search Forums section and type in Barracuda Headliner, Headliner Tips, Headliner Installation where you should find many of your questions answered. I put the roof rails on after the headliner install came back from the shop, didn't do the headliner myself. One thing I had to...