Posting the factory service manual instructions for future reference. Luckily, this platform included a fuel pump access cover in the trunk. Random trivia on the G-body: http://en.wikipedia.org/wiki/GM_G_platform_(FWD)
Confusingly, these ARE G-body cars but also C-body cars. C-body (in addition to H- and K-) is part of the G-body family, which is a little weird. Also of note, this family of FWD platforms is definitely a big step up from the ubiquitous W-body.
Anyway, here are the PDFs on replacing the level sender. The in-laws' has a schizophrenic gauge.
http://sdrv.ms/1kQsCZk