The parts book went kind of crazy with the abbreviations:
AT = automatic transmission
DOM = domestic
PT = positraction
HP = high performance (meaning 4 bbl carb)
CT = conventional transmission (meaning standard shift)
EXP = export
4400 means all LeSabres including the 4445 3-seat Estate Wagon.
The dealer brochure explains it a little better for standard ratios:
2.78 for 2-bbl automatic
3.36 for 2-bbl 3-speed standard shift
3.23 for 4-bbl automatic
3.42 for 4-speed standard shift
The 3.91 ratio was a special order probably used for mountain driving or racing.