Shorten Rear Diff - Need a little advice

It looks pretty good but all the shop needs is the flange to flange dimension unless you plan on centering the rear which it doesn't look like your going for. I would lose the old flange location and only provide the dimensions of what you want. The dimension for each side, passenger side from center of pinion to center of flange = 24.475" and from center of pinion to center of flange on drivers side is 28.725". I only say this if you decide you need to move it on one side more than the other. If your only doing what your print states just tell them to lop off 3.5" off of the ends and weld your perches 3.5" inside of that and include the new perch dimension you want (it's not on there now). But you'll probably find that your rear is sitting about 3/4" or more to the passengers side. So if you want your tire to sit dead center in the wheel well on both sides and your drive shaft to stay exactly where it was then you need to compensate for this dimension and have more cut off the passengers side than on the other. If you have them just cut off the 3.5" off each end your rear will be shorter but you won't be able to get the maximum size tire to squeeze in there because on the drivers side it will fit nice and even and the passengers side will hit the outer wheel house. Only way to compensate will be to get two different wheel offsets and that would suck! You can move the rear a little left and right with your perch dimensions but can't go crazy with it or your driveshaft may get close to the tunnel (not good). Hope I helped and didn't confuse anyone, any questions or clarification let me know. Been down this road, just trying to help if I can.