You may want to research that a little more, my GM catalog here in the parts dept says that the Lucerne (only 06-present) is a "H" body... the Regal in all bodies is the W body along with the Lacrosse/Allure so that would be your best bet.
Sorry bill I checked, no info for the wheel backspacing or splines available to me from any of them. I kno, fail parts guy![]()