Will an 8 1/4" bolt right in to my 7 1/4" spot?

""Will my current driveshaft work with this?" NO."..........why? too short? u joint wrong size?
"the cables could if they are the correct style. there are to styles, a single cable with an equalizer that connects to a long and short e brake cable, and a Y type that connects to two short cables."............so if my current style is the same as the new diff it will work?