I tried introducing 3 month old pullets (1 BuffO, 1 BlackSL) into my neighbors flock of 3 redSL hens and 1 Old English Game bantam rooster. The hens didn't even seem to notice the pullets but the rooster went hog wild. I don't know if he was trying to mate or what but it was brutal. After 3 days I brought them back home. We will try again in another 8 weeks.
Good luck!
Good luck!