Rear spoiler

Spoilers would have been nice on them cars but mopar skimped a bit in this regard. I would think due to the contour of the lid and such pretty much anything you attempt to retrofit will need tons of mods to get it to fit to the lid. It would seem by the pics these Cuda's, one a 68 and the other a 69 and on both the spoilers appeared to be simple and straight forward you may be going in the wrong direction. I am sure you can go to some aftermarket car accessory place that makes wings, fender flares and such and ask for some ideas.
Myself I would get an old trunk lid, 67 to 69 fastback should be the same on the lid itself and get a bunch of molding clay like they use when they build them concept cars. Lay a bunch on the lid and start shaping it to what you want. A large sharp knife, some bondo cheese graters, sandpaper and sponges and you can make one yourself. Remember to duct tape some wax paper to the lid first so you can remove the spoiler when done. Maybe take the finished spoiler to one of the shops I mentioned and see if they can lay down a mold and pop you out a few or do it all yourself. Gotta be cheaper that buying something and cutting it up and shaping etc and maybe less time too. If you do good maybe you could even have some extras made and sell them to anyone who wants something different. Just a thought.
Chas.