Starfury

67 and 68 spindles are different. 67 V8 spindles are the same, regardless of disc or drum setup. 68 spindles are not, and use a different single-piston caliper and bracket system than 65-67, which uses a 4-piston caliper that bolts directly to the spindle.

Al Newman

I stand corrected. Did not think of the disk brake spindles. Was simply thinking about the six cylinder spindles currently in place on the 1967. They are identical to non-disk brake spindles on the 1967-68 Cougar and simply need a V8 5 lug hub to convert them. If the Cougar has disk brakes and you want to use them, you will certainly have to transfer the spindles and all other front wheel hardware to the 1967 Mustang. My bad. Don't forget the prop valve.
Best,
Al

Mhegel

Next question is. Are the brake lines different from manual drum to disc?

Starfury

Slightly, yes. The lines to the distribution block and the lines from the block to the front wheels are slightly different, the latter resulting in a slightly different mounting point for the brake hoses. But I would never recommend swapping brake lines. Bending new brake lines is pretty easy once you realize how it works, and modern brake lines are designed with multiple layers to help prevent kinking.