Were these coil-overs spec'ed out for a Bronco? Or did you pick them up from someone who was originally going to use them for another type of rig? This can make a huge difference in where you end up, and be the difference between raising your Bronco up too high, or having it squat to the stops just sitting there.
What length of travel are they rated at? Obviously, to mount them to your hoops you'd need them to compress 12" under load to get to ride-height. No way for us to tell from here what you're going to get. The spring rates will help, but there are so many variables that you may just have to be your own guinea pig when it comes right down to it.
Paul