Dimensionally, the '72/down and '73/up LCA's are the same. There is a difference in how the steering stop is designed, between the LCA and knuckle. You can use either arm you want, but best to keep same generation of arm with the knuckle you are using. The front track width was increased 1-1/2" in '67, but the LCA's remained the same. All the increase was between the LCA pivot bolts.
As an example, if your early A (up to '72 is a sway bar car) then keep your existing lower arms because of the sway bar tab location. If it is not sway bar equipped, then swap LCA's with the big bolt discs, knuckle and UCA. The '73/up LCA's have the tabs mounted in a different position.
Hope it helps,
Mike Bynum