I have the book Buick Muscle Cars and there is a story about a fellow describing his rare car. The car in the picture is a WE4. Here is the text to the story:
...Finally there was a so-called Regal T-Type "Special T." Brock Fisher of Dayton, Ohio owns one of the rare versions and explains what it's all about: "I guess that the best way you could describe this car is that it's a 'half Grand National and half T-Type.' There isn't any Buick documentation that I could find that described how this model evolved, but the best I can figure out is that this car started out to be a Grand National, but they ran out of interiors before the end of the production run. Thus, they came up with this 'Special T' which used the Grand National body."
Fisher explained that he'd never seen another of the model. "There are probably a lot of people that own these cars that don't realize they are really different from the standard T-Type. But I want to emphasize that it is a legitimate variation, because the 'Special T' is called out on the window sticker."
The part about running out of Grand National interior is a crock because only the GN was built on the extended run. He also keeps referring to the T Regal as "T-Type" which we all know didn't exist in '87. The car is clearly a WE4.