From what I read they were offered back in 56. Looked and all I saw was drum for the 67 383 vert.
Now with 67 Barracuda the 383 got disc front and drum rear.
I'd guess your 383 is also like that.
I restored a 68 Road Runner that had factory Bendix 4 piston disc brakes. Car had many options, as it was an ordered car. Still have a set Bendix brand pads for that, for sale, in Carlisle. Nobody knows what they are, apparently