I'd go with the 69-73 factory spindles and 11.75" rotors.

The 73 spindle is the preferred one because the rotor is/was cheaper than the earlier 2 pce one. It is my understanding that they are machining the unicast rotor to fit the early spindle so they are cheaper than when they were 2 piece.

The only difference between the early and late setup is the bearing size on the rotors. All the other parts are the same.

Kevin