I know this is an old thread but I wanted to share this for the next guy searching for info on how to remove the dash on a 69 510. The previous owner of the Wagon had the Speedo, glove box, ash tray, and some other panels removed. I have never worked on an older car before and was very nervous about braking any of the brackets/mounting points. I ended up having to drill out a rusted screw connecting the dash to the firewall just below the left side of the windshield.
Now that I have this out, I will repaint the dash skeleton black, and recover the dash pad.