As far as I know all Panthers are 28 spline until 2005, then they went to 31.
1995 Grand Marquis LS (12/06 to 8/07)
1997 Grand Marquis GS HPP (11/08 to 12/09)
2004 Grand Marquis LS Ultimate (11/19-present)
98k and very, very slowly climbing
It's good to be back.