The axle itself will not work, because of the Ranger having leaf springs and Mustangs having coils. Unless you can fabricate and weld. However as long as you still have a 28 spline rear end, the gears should work since 99% of Rangers have a 28 spline rear end. With the exception of 01+ FX4 Level II's which have a 31 spline rear end. All Ranger axle's are still drums in the rear, there just are 2 different size rear drums ( which doesn't matter in your case ). All are the same width and everything.
Brenton