You can use the 73 and up disc brakes on you car and you don't need the 73 nd up upper control arms. Dr Diff offers some tapered ball joint adapters that slip around the small early ball joints and adapts them to the later spindle. They will work for you just fine using the early A upper control arms if you want to retain those nice disc brakes. Here you bees.
https://www.doctordiff.com/a-body-upper-ball-joint-tapered-adapter.html