I tried doing some searching before I posted this.
If you had a 1968 front bumper with only the specific holes required for a 68, would I be correct to assume that it is a GM bumper? On the same note, if you had a 1967 front bumper with the 1967 specific holes, would that be safe to say it's GM? My thoughts are that the aftermarket might have added all the 67/68 holes to only have one bumper replacing two....Joe