Had the same issue with my 68 Roadrunner. I bought the 68-70 clips from a vendor and they had the short clips.
The old clips from the car were the long ones. I called Jamie at Mega parts, and he told me that a lot of 68 use the long clip, normally found on 66-67 cars.
I reorded the clips and used the long ones, they were correct for my car.