Jeff the data on my front bumper , 9/19/68 built NJ car, is stamped on either side of the nose/peak and in line. 8 26 1 on one side and probably is Month Day Shift. 68 M 9 is on the other side. The 68 has no separation between numbers as in the 65-66 examples, so, I am still unsure of the Month Day designation. The M for Monroe and the 9 for 1969 works. This would work better if I had some photo/examples and when the bumpers come off, not planned, I'll get the pics to you.
The numbers on my rear bumper are not readable with the flashlight/mirror trick but I can see the indents in the chrome side, four, they are in line and between the tag light screw holes.
Thanks for your patience and interest. Brian