One other thing to be aware of which is true on 79-85 and is very likely true on your 76 as well is the idler arm adjustment height is critical. There's a measurement taken at the control arm and that measurement should be as close to perfect on the idler arm side versus the pitman arm side. Improper adjustment strongly influences "orbital steering".
You may also want to see if there are other worn parts. My 79 Toronado has a tendency to wear out idler arms. I recently replaced the existing with the Proforged version as I've been pretty impressed by their parts if they exist for your particular vehicle.
Good luck and let us know if you find the root cause,
Scott