For any explorer rear swap on a ranger, you'll need to weld on new spring perches and shock tabs.
The reason is because explorer leaf springs are BELOW the axle, where as a Rangers springs are ABOVE the axle. Also, the spring plates on an Explorer have an integrated shock mount that will not work on a ranger. So some welding is required to bolt in an expo rear end.
4.10 expo axles are kind of harder to find...I've only ever seen 2 in my years of yard hunting.
Check out www.car-part.com
An alternative if you're only after discs would be to bolt on 95-04 Mustang GT or Cobra rear brakes. Below is a link to all the info you'd need.