Power box

Yes in 1973+, all the bodies changed to the larger sector shaft one, which was always used in the C-bodies (at least my 1965). The shaft diameters have been posted many times, so search. Might we ask why you care if you have a 1963 already? Another change was the direction (up or down) which the tie-rod studs pointed. I recall it was upward until 1967, so if yours is thus you can be assured you have the early box & Pitman arm, indeed must be since 1967+ cars had a wider body and thus different steering cross-linkage, but verify by googling images.