There are different types - some with a separate bolt that can be undone to change shocks without having to remove the bolts that always break and other (like JKS ones) that require you to remove those bolts each time. The first type generlly give about 1" extension to the mouting point and the latter less, maybe 1/2".
I guess we are talking rear upper shock mounts on an XJ here? - Once you snap them and re-drill and tap the holes, if you install replacement bolts with copper grease you probably won't have a problem again.