Someone may have more correct info, but I think there may have been dimples in the pan for locating the screws on those cardboard boxes. Also, more often there was only one box and on the passenger side, depending on year and options. See UPCs U57 and U80, plus U79 for 1968 and 1969 in the assembly instruction manual for your year. If you have a 67 you can look at the cowl trim tag to see if the car had U57 or U80.