That T-Bird trans should be a 4R70W - 1st year they started with that
trans in the T-Birds.
Mr Ford is correct about the bellhousing pattern of course.
However, a 4R70W from a 3.8 V6 Mustang (you'd want a 98-up cuz of
the internals) WILL bolt to Windsor V8 and only have 1 less set of direct clutch plates than the mod motor V-8 model, which is a really easy add.
You'd want to go thru and check/freshen a few things anyway to any used
trans, do a little mod to the vb
Here's a bunch of info on those transmissions and how/what to do
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