That said. I'm sure a 74 duster car cover will fit over a 66 Barracuda. A form fited California Car Cover for a 66 Barracuda will fit more snug in certain areas. But a 74 Duster will fit pretty good since it's a little bigger everywhere and has a fastback like roofline.
I was 100% sure of that but was wondering the pther way around the smaller Cuda cover on the larger Duster