So as I found out today as I went to install a set of completely re-bushinged and boxed control arms on my 69ss. I used a set off a parts car so I could take my time and have as little down time as possible. When I went to install them I noticed that the drivers upper arm was rubbing on the top of the diff housing. Upon closer inspection the 12 bolt arm is cut short and has a reinforcing plate on it where it is shortened. So now I will box it and press the bushing out of the other one and press it back in this one if I do not tear it up in the process.
Rant off
So beware.