Driveshaft length 8 3/4

Going from a 7.25 to a 8.75 rear end will require you cutting your drive shaft down some. I dont remember what I figured it to be on a 66 Dart GT with 8.75 and 904 trans mission. I can get a measurement if you need. Just measured it, it is 54 inches from the center of the rear u joint to the center of the front u joint. It could stand to be little shorter but that measurement works for me.