Usually the 31 spline axles have a 3.25” tube OD, measure the one he has.
If 2.75 or 3” (can’t remember) it is a 28 spline unit.
If his is a smaller tube unit look for an Explorer Rear Differential Housing… 4.10s, LS, 31 spline axles and larger axle tubes and some have disc brakes. These can be had for around the $150 mark so shop around. TheExplorer Housing will need a little work of remounting the spring perches and shock mounting OR you can buy a kit so there is not welding and will make this housing ALMOST a bolt in.
4x4, 5sp, Std Cab, Stepside, E4 Red
4” Lift - Coil-Overs, 6” SkyJacker Leafs - No Blocks (Mistake)
31 Spline FX4 Rear Axle, 4.56s and OX Locker, Hurst Shifter w/Optional Stick and "Made by Grev" alignment adapter