With the exception of the new pickup, this really has nothing to do with T-Birds, though the body design is a my interpretation of a T-Bird crossed with a Danelectro Pro. (that and I do have a short scale Asto-Bird in the works...); I originally installed a GFS lipstick tube humbucker in this bass, but I wasn't impressed with the tone. This is the bass with original pickup:
Ultimately I decided to install a Gibson Les Paul Bass TB Plus pickup (basically a T-Bird pickup in a humbucker casing). Unlike the guitar pickups that are in the Epi limited edition basses, this is an actual U.S. made Thunderbird bass pickup (this pickup is either a prototype or at least a very early 90's model). Here is the underside of the pickup:
I am really pleased with the results. The T-bird pickup is a really good match for the semi-hollow body; I was worried about having too much mid range (I'm a P-bass guy at heart; love the T-Bird growl, but it doesn't sit in the mix like a P-bass... Sorry

), but this combination has a lot of bottom end with a bit of "twang" when played with a pick... Perfect (for me)!:
Moonshine