2&3 are hold down clips for the main wire harness and 1 is for the ground. The EF would go in the hole on the LH side that the top arc of the circle you drew around #2 is all most covering.
Marty - it looks like there is a bare sheet metal bracket at a 90 degree angle to the dash face. I've updated the picture showing that as hole #4. Is that the mounting location of the emergency flasher unit for late 67/68?
If that is the case, I still have questions:
1. How is that bracket attached to the dash substructure, seeing that it is unpainted it is a separate piece. (The early 67 does not have this bracket, as described and pictured earlier. The clamp is attached precariously to the #3 hole ground screw on the back side of the dash structure. Probably the reason for change)
2. Was the metal "spring clamp" that the flasher unit snaps into then screwed into this bracket? Was the spring clamp unit directed towards the driver or passenger side? Were the electrical connections facing the driver or firewall?
3. Last question (this time around) - switching from the emergency flasher to the turn signal flasher, what was that physical location? Again, early 67 was on the rear of the IP.
Thanks!