[Cracker289]

You know the trim that goes along the bottom of the car, beneath the doors, on a 66 it has 3 or 4 black lines in it, but the 67-68 style is smooth. Can you use the 67-68 style on a 66 coupe, or is the length and/or width different?

[not2brite]

I've been thinking about doing the same thing. The only things I know for sure are:
The wheelbase on a 66 and 67 Mustang are the same.
The wheel opening shapes and curvature of the rocker panel are slightly different.
You really won 't know if it will work for you til you hold one up to your car.

One other issue might be mounting hardware. Not sure if the holes will line up and the actual clips will interchange.