rear end question?

the rear end on my 70 d100 locked up today then threw the drive shaft. the rear is completly locked. im hoping to just get a near center chunk and replace it. i need to know how to identify the rear i have and any info on how to change the center would be great. this is my daily driver so ill have to drive my valiant till its fixed and the gas is gonna empty pockets real quick thanks.:wack: