1986-1993. The 1994-1998 can be bolted in, but they are slightly wider (about 1.5") I don't know about the 99GT+
The 1987-1988 Thunderbird TC is known for having the 8.8" rear end, but it's not a direct bolt in with disc brakes. It's also a little wider than the Fox chassis, and I'm not sure if the quad shocks mount in the same location.
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