The best part of the Explorer Axle swap is the 31 spline axle shafts, comes with a limited slip and you can find them with disc brakes, which are far better than drums. Most Ex-Axles are 3.73s some are 4.10s.
Either choice will need a little rework to fit in but there is a kit for the Explorer Axles to make them a bolt in.
Most Ex-Axles can be had for a buck and a half or less.
And then there is the FX4-LvL II Axles, is you can find one but I do not think you can find one for less than $300.
Is the Mustang Axle the same width as the Ranger ?
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