Just use the spindles from the later model truck (73-87). You are going to want the early ones with the 1 1/4 brake rotor. If you want to keep it 6 lug you can order some rotors from summit for $129 for the pair. You will later model ball joints that will fit in your 64 control arms and outer tie rod, you will need a tie rod sleeve that accepts the two different size tie rods. You have to switch the original outer tie rod to the inner position. I did this to mine not to long ago. I have also used the entire front suspension from a 75, and the control arms will bolt to your 64 cross member. You will have to use the entire front steering components if you want to use the later model control arms. It is a lot more work.
http://www.67-72chevytrucks.com/vboa...isc+brake+swap