L78 = Pontiac 400 base engine (no W72 package)
L80 = Oldsmobile 403 engine
Y82 = Black and Gold Special Edition with Hurst T-Tops (In '76 it was used for all S/Es whether they had T-Tops or not) '76 through mid year '78
Y84 = Black and Gold Special Edition with Fisher T-Tops Mid year '78 through
Y88 = Gold Special Edition
You can go here for more info on the S/E cars.
http://www.78ta.com/special.htm