Hood ornament is different between sixes and eights, on the side panels the sixes have a shorter grille with Pontiac script near the headlamp, the eight's side grills continue where the script is on the sixes. On the bottom of the silver streak about even with the bumper blade the script across the silver streak says eight.
Eight;
http://www.collectorcarads.com/Picture1/DSC08647.jpg
six;
https://upload.wikimedia.org/wikiped...Sedan_1938.jpg
Also below the script on the lower part of the silver streak ( down by the front bumper ) The chrome grille continues down where the six at that juncture the last lower part of the grille is painted.