First off, I'm new to these trucks so please excuse the ignorance of my question. I tried doing a few searches but couldn't find what I was looking for. My girlfriend's dad has a 72 Chevy that now has a 454 with (I believe) a 4.10 rearend. The engine's built and puttin out plenty of torque so he no longer wants to use that rearend. He does a lot of freeway driving so he wants something that isn't as steep to get better mileage. Question is, what differentials came on the 72 and what are some direct replacement options we could find at any old junkyard for cheap? Thanks for the help.