? on 7 1/4 to 8 3/4 rear end

Whats in it for a transmission? I just put a 8 3/4 and a 727 in my demon(108" wheel base). It was originally a slant 6 with a 3spd manual. I had to cut it to around 46 1/2"
When you get everything in (tranny and rear) push your slip yoke in the back of the tranny all the way, then pull it out about an inch, then measure from the center of the caps in the slip yoke to the center of the caps in the rear yoke. That should give you the length you need