the case of the diff has several holes with which ot mount the diff to the beam
they are all the same on the 7 and 7.5 diffs other than one at the very top, which is further out on the 7.5 diff
however, the bolt that goes through this runs from side to side so you simply chop a bit of the casing off to effectivly shorten the tube the bolt has to run through
also, the granada and sierra diffs are slightly different throughout the years as some granada diffs had 2 long bolts going through whereas the sierra had bolts that went into the diff and not through
this may explain things a bit better
see the smaller diff having a hollow section where you can see the bolt going through while the bigger one hasn't?