The 67 and 68 F bodies have the screw connections on both ends. I've also run into the same problem with the parts stores (AutoZone) saying the speedo end is a clip.

Your cable is correct in that the inner cable can only be removed from the trans end. I never heard of that causing problems, however.

I took a chance with whatever Ames had. It was just a few inches longer than what it appears to be on the car now. Of course, I had to measure it installed, so I might be off a little. I think it will fit OK. There appears to be a lot of wiggle room. Don't know about the quality.