it is simply a vinyl top OPTION on the BH29 Barracuda fastback - available in: V1X black, V1W white, V1F green, V1T tan (NOT AVAILABLE in "Mod Top")
"slickback" is just a fancy marketing word for the brochure - it found its way on to roughly 9.5% of fastback production
Wiki refers to it on some Chrysler models as
"canopy" style. Don't know if the "slickback" fits this category or not??
https://en.wikipedia.org/wiki/Vinyl_roofCanopy - in this style, the vinyl covering is applied only to the front half or two thirds of the roof, usually ending at the trailing edge of the rear side windows. The windshield pillars are very commonly covered in this style, but the C pillars never are.
Mike