Look around for the spindles, backing plates, & disc brake brackets! Buy new rotors ,calipers, pads, & brake hoses. You can save a lot of money doing this. I found a complete outfit at a reasonable price the other day off of a 70 model Pontaic Lemans.
I have a 68 that I put front disks brakes on, I bought a junked 74 Nova for $150 I bought new pads, hoses, had the rotors turned, put the whole system on i.e. booster, and it works way nice, and bolted rigth up. Also I have read that you need to avoid the really hard stops for the first 100 miles or so for it to all seat.