Do you own Jerry MacNeish's 'The Definitive 1969 Camaro Z/28 - SS396 Fact Book'? This should be your first place for answers.
An early build SS Camaro would have 2-piece rotors, single piston callipers. My 10-D-68 build SS Camaro has a '309. That is the number
you should be sticking with.
Steve