Welcome to the forum
Looking good
I can't believe how rust free this truck is either. Yep the '63 12 bolts had pressed on backing plates. You could probably cut them off and try and weld on some flanges to bolt the caliper brackets to, but they will have to be absolutely true to the axle flange. It might be easier to swap the differential for a '64-'70 truck 12 bolt. Or if you are going with 5 lugs, a '71-'72 would be a good swap. That is if you can find one.
No matter which column you use, it will have to be modified/shortened for use with the power steering.
Let me know if you need the steering box adapter plate.