Explorers are 5 on 4.5 so don't bother with that. also, you will have a 31 spline big bearing. no need to wonder. the big question is roller bearings or tapered bearings, but that only matters if you're replacing the bearings or seals (which are integral with the bearings and the bearings are press-on and have to be done by a shop)
I believe the guy that did mine used CJ front rotors and chevy cailpers, but not sure. here's a couple links for 9" disk conversions.
http://fordfuelinjection.com/bronco/brakes.html
http://www.pirate4x4.com/forum/showthread.php?t=229934
The rotors I have didn't fit perfect though. see the slop around each lug?
the previous owner did nothing about it, but I couldn't accept it. So I went to the hardware store, found some small spacers (essentially a short tube with a specific inner and outer diameter) and sliced them to length so they fit around each lug.
does a great job of keeping the rotor aligned and centered. :thumbsup: