x2 on what Brooks said. Also need to know a few other things before you can dial in what you need and where it needs to go. Assuming since you are referring to coilovers, should we assume you are linking the back end? If you are, are you also considering running coils and shocks instead of the coilovers? Are you stretching the rear?
If you are just looking to run longer travel shocks with you leafs, you might just want to consider adding ford f250 brackets and just frenching them into the frame. A rule of thumb for the location is use a square and put one of the straight edges on the frame and move it until it contacts the center of the axle tube, this mark would be the center for you frame side mounting location.