More information on the LaSalle II sedan can be found here. It was much smaller than standard 1955 American sedans, having a wheelbase of 108 inches (2,743 mm). This was the same as that for GM's eventual compact car entry, the 1960 Corvair, or more currently, the 2001 Ford Mondeo.
Both LaSalle show cars were to have been destroyed, GM's usual policy at the time. But they managed to survive, badly deteriorated, to be acquired by the Bortz collection of concept cars. The sedan's entry on the Bortz web site is here.