I integrated two flocks last year and it was a LONG process of observing and mixing up who was with whom! I did about 4 different variations of caging up pairs and who was likely to be aggressive and each of these variations lasted about a week. I let the newbies and the least aggressive hens free range for about 4 days. The more aggressive ones had to remain in the run and coop while the others were out. The gotten shortened later in the day free range time and I put the other in the run, coop--swapping spots. Then I mixed one of the more aggressive ones in, then finally my top of the pecking order got caged each day for about 4 hours within the coop. Eventually she was let out too.
The tips about multiple feeding stations worked really well for me--I had 4 feeding stations for 6 hens for about 3 weeks. Also the tip about treats worked well too. As long as each hen had an area for their special food, they weren't as aggressive.
Our lowest pecking order hen is still a bit pecked upon but she manages and she knows to stay away from the one who will pick on her. I also fed her more (separately) during this stressful time so that she had energy to deal with this.
Good Luck!