If the 63 is a 6 cyl which has a 1" shaft in the steering box then the 65 falcon or mustang pitman arm is a direct fit to the steering box. But you would need the other steering parts including a 65 falcon centerlink to fit.
If it is a v8 steering box then you would need the pitman arm from a 67 to fit.
I will check the arm to see if it has any markings. I cut the arm in half as I was pulling the suspension out to do the MII swap, then decided to do the swap on my fairlane, so I'm putting the falcon back together.
I believe the car was originally a 6 cyl , 3 spd column shift, has a 302 and C4 in it now. Again, will check for numbers on the part.