D'oh, I just realized- the 13" BH36829 is for V6 cars. Which makes sense- the 7.5" rear end and all... That's why it didn't come up under RockAuto's 1995 5.0 section. It's right there under the 3.8 section. So yeah you don't want that (unless maybe you're building a lifted off-road machine lol).
Amazon and RockAuto both list that Centric 150.61328 as being a Cobra-only part, but RockAuto doesn't confirm its length as being 15". Why would the Cobra's be different from the GT here? I thought they didn't have IRS until '99 models.
Sounds like the one you want is the BH38372 (or whatever equivalent brand suits your fancy).
1995 Mustang GT (5.0), daily driver
1995 GMC C2500 (5.7), alternate daily driver