You don't need to change the column signal switch at ALL. On the 67, the hazard outfit is completely separate and basically "splices into" the signal system. Now I realize it plugs in, but it hooks in as if it was an afterthought You used to be able to buy 4x hazard switch kits that work the same way.
One of the add on 4x flasher kits you used to see:
All in the word that a 67 hazard switch, is the following:
A 3 pole, single pole switch. (3 pole means it is 3 switches in one box, NOT 3 terminal)
So you have 1 input, 4 outputs. The 4 outputs are all separate with switch off, with switch on all 4 terminals are hooked together
The 4 way flasher output hooks to the common switch contact
Then the other three (open) switch contacts hook to:
left front signal wire
right front signal wire
brake light switch output on it's way into the signal switch.
Below is a functional diagram. Everything inside the dotted lines is added 4x flasher circuit to a car which had none, or also the functional way that my 67 works
In the screenshot from the shot manual, that's exactly how my 67 is wired
The 4x flasher gets power from the fuse panel at very top. Power out of the flasher comes down the page on D32 to the switch. This equates to the right hand part of the diagram in my drawing
Then the other three terminals equate to the left hand terminals of the switch in my drawing
D9 and D9A top right terminal, tan, go off to right front signal and right indicator lamp
D10 and D10A, top left terminal, light green, go off to left front signal and left indicator lamp
D4, bottom right terminal, white, go up and branch into the output of the brake lamp switch. So with the switch centered, this power feeds both rear lamps