73 disc brake, and all 74 up lower control arms have a different deeper taper for the larger lower ball joint than the 60 to 72 disc and drum brake cars and 73 drum brake.
That is an inaccurate, untrue statement.
You are trying to pass along wrong, false information.
Whoever told you that, doesn't know what he's talking about,
ALL 1962- 76 lower control arms are the same thing, and will interchange on all the A body cars.
The only thing that changed are sway bar mount tabs for 65-72 cars, and then 73-76 cars, and where they are welded onto the LCA itself.