W5 is a 3.27 open rear end, I had the same in mine from the factory. As far as parts all you need is a trac lock IRS specific differential, and drop it in. Simplest swap you can do to get trac loc is find a SC in the boneyard and snag the pumpkin. Its a direct bolt in swap. Next best thing to do is come up with the IRS trac lock, a Mark 8 aluminum pumpkin and whatever gears you want and have the whole thing assembled fresh, and then its still a direct bolt in swap. Just an FYI, the Explorer IRS or any straight axle trac lock wont work for vairous reason without modification. Yes they can be made to work, but they need extra work. Your best friend is an SC in the yard and/or a Mark 8, even though the Mark 8 got 3.07 open rears, they had the good aluminum pumpkin, or find a 99-01 Cobra rear as they had the 3.55 aluminum 28 spline trac loc rear that bolts right in as well.
Ban low performance driver's, not high performance cars.
"Any idiot can make a Mustang fast, but it takes a special kind of idiot to make a Thunderbird fast."