8 3/4 741 case questions.

Now that I have my 8 3/4 I am kinda question whether or not it was such a good buy. I have been reading some info and looking up prices of different parts today and I am not thrilled by what I have found. If the 741 case has a 1 3/8 pinion and the 7 1/4 also has the same size pinion what the heck am I actually gaining? Was looking at Mancini's site to get some prices. For detroit lockers they don't specify for which case they are for will a detroit go into any case? Also who makes gears that will go into a 741 case? Also can this 741 case just be gutted and replaced with all 742 parts?