Look on the drivers door edge for the Safety Standard Cert. Label
There will be an AXLE code number like 87 or R6
Go here to look up Ranger axle code: Ford 7.5 & 8.8 Inch Axle Tag & Door Codes
Open = standard axle(only 1 wheel spins)
L/S - Limited slip(both wheels spin if you get stuck, lol)
Limited-slip differential is the generic name, posi-traction is what GM calls their limited slip differential.
There are also locking differentials, these have a selectable "control" that physically locks the differential so both axles spin at the same speed, great for traction but bad for going around a corner on a hard surface.
L/S is a compromise between open and locked differential
Front axle/differential will be the open type no matter what rear is, but it will have the same ratio as the rear, i.e. 4.10, 3.73, ect.....
Lowering tire pressure is a must in the sand, you need a wider softer footprint to stay on top of the sand.
So a portable air compressor or an air tank is handy to have, so you can refill tires and make it to the closest "real" air compressor.
Also in the Oregon Dunes parks a red flag 9ft above the ground is required on all vehicles.
And I believe you need a permit now as well.