Modifying the rear bracketry to pull the wheels in really is only needed if you are running 9" or wider rear wheels.
Since GroverDill has already committed to running a version of a Ford 17x8 wheel out back, it's not an issue to keep the SN95 width axles. In fact, the extra 0.75" out will help fill the wheel wells better. I have some old pics of 17x8's on my old 5-lug drum setup and the look was horrible. Rears were VERY sucked in. His decision to run the Sn95 axles in this case is the correct one.
EDIT: Had to dig waaay back for this one. 15-20 year old pic of my car with the '97 Cobra wheels and 5-lug drums out back. As you can see, those rear wheels are VERY sucked in.
Now, compare the above to the pic I posted here with 17x8's and the SN95 cobra rear disk setup.