In that case the coil springs are the key - it's the P30 chassis rather than the W20/W22. Yo will also have a 4 speed Hydramatic automatic transmission, whereas the W series has a 5 speed Allison in that model year. Your chassis GVWR should also provide a clue - the W series chassis will be either 20,000 or 22,000 lbs, while the P series is 18,000 or less.
As far as I know, none of the 27's were built on a W22, though some of the longer Sunovas were.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL