You already have an 8.8 rear end. All 87up 5.0 stangs do. No upgrade necessary there.
Now Im going against everyone else, because they have not looked ahead. 3.73's would be better for you at the moment. But as your going to add a blower, and increase your trap speed to probabably 120-124mph, your going to need to be able to cross the traps in 4th gear with a 26" or 28" slick. I believe 3.73's maybe a bit much with a 26".
Skyler
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-1989 Saleen Mustang #406- TFS Heads, E-303, edelbrock intake,70MM TB, 73mm MAF, off road H, headers and 3chamber flows.
12.55@107mph
50-175 Nitrous Works WET Kit just added.