well, he's only in with two hens (18 month old, not pullets) and was introduced to them one at a time. There's no sign of the hens giving him a hard time and although penned, they have plenty of greens, perches and are on breeders pellets. He looks healthy enough and I wormed them all about a month ago.
I will maybe go back to the breeder of the hens, see if she has a different strain and can let me have an unrelated cock. It will be a shame if I can't breed them this year but not the end of the world.