1973 Duster 9 inch brake upgrade questions

If the upper ball joint's flats are wider, then it is the bigger one. Seach for the special socket and they give the 2 sizes to compare. Perhaps the factory started putting the 1973 upper control arm in drum cars and machined the holes in old stock 9" drum spindles to match. A prior owner might have done so also, though machining a tapered hole is not simple. Someone with a 1973 9" drum car may chime in. Many confusing things were done during transition years to use up old parts. Best guess on the 10" rear drums is that someone swapped out the whole axle.