pre 90s ranger, i would assume its a 7.5, even if it were an 8.8, all stock ranger axles were 28 spline unless its a fx4 level 2 axle which would make it 31 spline.
did you buy it with the lift installed already? if you did, are you sure its the stock axle?
running 33s with a 2.8l and no re gear, that thing has to run like a dog! i ran 31s with a 2.9l without regearing and it ran dogged as hell. if you do swap anything, go for an explorer axle and regear it. all explorers ran 8.8 31 spline axles.
hope that helps. check out the tech library for more info on how to identify
