Explorers are 5 on 4.5" , just like most Mustangs.
The 8.8 is a good rear end, as for which ones have a limited slip, I'm not too sure. If you spent some time researching you may be able to come up with some sort of VIN decoder to figure out which ones had the LSD's. I would not rely on that solely, you may want to hand pick one at a wrecking yard, because the clutch packs may be shot. The spring perches could just be cut off. then you could setup your used axle with new perches to get the pinion angle and spring spacing perfect. It isn't that big of a deal, you could cut off the old perches, grind them down flush, then set the new perches (only a few dollars each, just measure the diameter of the axle tube, and the width of your leaf springs), get your pinion angle perfect with a protractor. Then just tighten down the U- bolts and weld it up (or use a free tow from your AAA card to take it to a welder).
Peter