I've been checking around, and checking into the possibility of using a good quality barred rock hen to improve size and type in my SPPR flock as well. From the folks that I've spoken with, who have a very good working knowledge of poultry genetics, nutshell version I got was that yes, it can be done, but that it would take as long or longer to get the pattern back into the bird than it would to just keep breeding your best pullets/hens back to your best cock bird. At least, though, the size issue woudl be resolved likely in the first generation!