I'm not sure why you would be interested in keeping the spindles, but I assume you know that both rotors and calipers will need to be replaced. The 67-68 GTO's used Corvette brakes (i.e. 4 piston fixed caliper), so I'm assuming it isn't to give the appearance of originality. You could probably find a take-off set pretty easily from someone who has done a suspension upgrade at a place like pro-touring.net. Any 69-72 A-body should work, I believe.
Hmmm. I don't think the '67-68 4 piston set-up were the same as Corvette 4-piston disc brakes, although they are a 4-piston design like the Corvette. 1969 and up used the single piston which in my opinion is just simpler in design.
You did not say if you have power drum brakes or non-power, or if you plan on using non-power disc or power disc?
What can cause a problem is the size of the rotor you use. Larger rotors will not clear some factory sized rims, and some will require aftermarket rims for use. Another problem can be rim width. You may need a wider rim or different rim offset so brake parts do not rub on the inside of the rim.
Not a brake expert on all this, but you also want to make sure you have matching master cylinder, proportioning valve, and any other needed parts.
- You can do a complete A-body disc brake conversion which requires the disc brake spindle as the drum brake spindle is different. You will need to grab everything as a complete set-up as there can be differences in years and you don't want to mix & match parts.
- Aftermarket. Many suppliers offer a conversion kit. Some install without problem, some seem to have a few snags that create problems.
Checked out the Scarebird set-up which looks like it will work, but you will have to supply the needed rotors/hubs & calipers. It also sounds like the rotors recommended may be smaller, 10.25" than the factory 11" rotors.
You may want to read the first post found on the Chevelle website. Gives a pretty detailed view of options and parts. https://www.chevelles.com/forums/16-...on-basics.html