Gibson part numbers 13531 (front), 13530 (back). The Bicentennial Thunderbird pickup is a sidewinder, like the EB and Ripper, but is designed for a brighter tonality. It has just one Alnico magnet, rather than the two of the EB and Ripper. Note that the 1970s Gibson Thunderbird bass pickup has three screws going through it, whereas the 1960s version had just two
Note also the chrome surround, held in place with six screws - a feature of 1970s thunderbirds only.
List of Gibson bass guitar pickups