I don't have both in front of me right now, but I'm almost certain that the 68 plate has more rounded edges on the chrome lower edge across the bottom below the radio. There were a handful of changes to make the interiors of the 68 safer (less sharp edges and corners) and this was one of them. The radio delete plates are also different, but both have a 67 engineering number with a difference suffix ( -a and -b)
John