I saw this post of mine from September and thought I would give an update.
After buying a second coop and allowing the rescue chickens a couple of weeks feeding and getting their strength back we mixed the two. Yes there was a period of sorting out the pecking order but nothing too bad. The originals stayed in their coop and the rescues stayed in their coop but the all laid eggs in the originals coop.
Now I cannot tell the difference between originals and rescues, the transformation is amazing and they have become one flock. Recently I closed off the rescues coop and they have all hunkered down together.
Trouble is I have now lost one of the originals to a fox and have been given 7 new (slightly bigger) chickens. I have extended the chicken run and am back to having the two flocks separated. I will give them a couple of weeks and then let them at each other for an hour at a time (under supervision) before removing the separation between runs.
The only trouble - what do I do with 11 to 13 eggs a day