you need to shorten your drive shaft 2 1/4" when going from a 7 1/4" rear to an 8 3/4" rear + 4 inches for the 727 . and if you dont already know, you need a 29 spline yoke for the 727. i went from a 225/ 3 speed/7 1/4 to a 318/727 keeping the 7 1/4 and needed to wack four inches out of the driveshaft. i will be changing it over later.I have switched from /6-904-7 1/4 '72 Duster to LA-727-8 3/4. I'm in need of the cap to cap measurement for my driveshaft.