I do apologize if this question has been asked over and over again. I am trying to basically rebuild a truck on a very tight budget. My question is, if my truck has a 8.8 rear diff, and I am going the route of swapping the entire diff from a used one purchased, does the replacement have to be 8.8 or could it be 9.75 as long as the gear ratio is the same?

 

I can't give you a definitive answer, but the two big things to ascertain are 1) Is the driveshaft the same length and yoke/flange configuration? 2) Are the parking brake cables the same?