67-72 disc spindles are all the same but the drum ones from 64-72 are slightly different but can be machined down to accept the disc brake caliper bracket. Thats what all the disc brake companies used to do years ago.
Although the caliper bracket is different from 67-68 because of the 4 picton caliper the spindle is the same from 67-72. The backing plate and caliper bracket are 67-68 and 69-72. the valves are also all different.
here is a link
http://www.inlinetube.com/disc%20bra...ion/dbrake.htm
or article
http://www.inlinetube.com/install%20...y%20Valves.htm
The first year for disc brakes on GM A-body products is 1967. All cars before this point in time had four wheel drum brakes. Disc brakes were introduced as an option from 1967-1972. Starting in the 1973 model year front disc brakes were standard and front drums were no longer available. When disc brakes were developed so was the dual master cylinder, so all 1967 and newer cars had dual masters. Disc brakes required different pressures so the master was divided into two halves to provide pressure to the front and rear separately. This also meant that if a front line blew out the car would still have pressure to the rear brakes and vise versa.
The first thing we have to clear up, is that all 67-68 Factory disc brake cars came with dual piston calipers, if the car is a 69-72 it had single piston calipers. Most after market sets come with the later 69-72 single piston calipers but this is not technically factory correct for the 67-68 cars. The single piston setup will bolt on all the 64-72 GM A-body's. The first issue to converting a car to disc brakes is what kind of car is it. If the car is all factory correct and that is a concern, single piston calipers on a 67 or 68 car will certainly catch the judges eye and throw up a red flag. If the car is a driver or modified car no one will care if it has the single piston or dual piston calipers. The first question we ask at Inline Tube is are you looking for original appearance or are you looking for something that just bolts on and appearance may not be an issue.