There aren't any OEM 6 lug rotors that will fit those spindles. The only 6 lug rotors that will work with those spindles are the aftermarket ones from suppliers such as CPP and ECE. If you want to stay with OEM parts and 6 lugs, you'll have to use different spindles and calipers as well as different lower control arms. That is all explained in the thread that markeb01 posted.
BTW front disc brakes weren't available until '71....just so you know when searching for parts.
