727 Kickdown

The Bouchillon kickdown is the way to go.

I currently use Lokar and have used it on several cars. A couple things of note with Lokar. Make sure you're using the shortest kickdown arm on the transmission, there's many of varying lengths. If you have one of the longer arms you can drill a new hole closer to the pivot point. I'm not sure of the exact distance but I know it's been posted here or at Moparts.

Also some transmission kickdown arms have a good enough spring inside to return the cable, and some don't. On my car right now I had to add a very light return spring to get the transmission to downshift more consistently as the arm itself didn't have enough spring pressure to fully return 100% of the time.