Here is a thread about using a 69-72 emergency brake pedal in a 67 cab.
http://67-72chevytrucks.com/vboard/s...d.php?t=751824
You should reinforce the area where the pedal assembly attaches to the firewall. You could just use a plate welded to the inside of the cab. For the foot pedal assembly GM redesigned this area of the fire wall by adding a raised area which strengthened that area of the firewall.
As stated you will have to shorten the pedal assembly where it attaches to the dash. I cut mine down so the mounting hole became a slot. Then drilled the hole in the bottom edge of the dash.
Also you will need to cut a rectangular hole for the cable to feed through.