I know the '65-'66 pedal is not a direct fit in a '67. Mustang Steve can modify them for use with his cable clutch kit, it involves the normal addition of the quadrant, plus modification of the pedal stop and the hangar bracket to make it work. He uses the early pedals sometimes because the '67 and '68 pedals are much harder to come by.
If you are using the stock clutch Z-Bar and all that jazz, it would be simpler to use the '67 pedal.