According to Auburn Differential the end of the axle changed after 1983. I had them on the phone this week after I got your PM about your hydra loc. Now I haven't dug out my Factory parts catalog yet but if what the guy at Auburn Differential is right then that means that an 84 axle will work. {I just double checked their catalog & the installation instructions too} According to them the change was after 1983.The 8.25 will interchange. The end of the axle never changed. Bigdad's truck having a 318 will most likely have a 8.25 Bob