Doing Spring cleaning in October and we have a complete disc brake set up for a 66 GTO. We will not use four piston GM calipers but wonder if there are any "100% nuts" that would want such a thing. It will not cause any tears to throw it in the iron pile.
Yes, they are desirable for a correct restoration. I do ground up concourse restorations on MoPars and finding original date code correct anything is great, including disc brake setups. For example, finding a set of C Body disc brake setups with correct Hardware and spindles by Budd is big money.
Disc brakes were not a GTO/Lemans thing until 67. I don't have my rt hand raised all the way up on that, but it seems to be what I recall. 66 was Chevelle SS and maybe the Buicks. The value is that they're a nut and bolt upgrade to a 64-5-6 GM A-Body car. Another don't quote me gig, I think the spindles are different too (also Chevelle).
I believe 1967 was the first Chevelle disc brake option, with the Rally wheel being introduced for cooling. Mick