I'm fairly certain that this can be done. I know they make a longer tailshaft version of the T56 Magnum for the late model Mustangs, which I think has the same bellhousing bolt pattern as your GT500 engine would have.
Below is an excerpt from a popular Mustang site's ad for the T56 Magnum. Based on this, I'd say you just need the correct bellhousing.
Tremec T56 Magnum - - With the appropriate QuickTime Bellhousing, this transmission will bolt in behind your 5.0L or 5.8L small block as well as 4.6L or 5.4L modular motors