Have you considered bantam cross-breeds? Bantam dark Cornish roo over bantam Brahma hens, or other breed? The reason I ask is that usually if you're using heritage breeds, a cross of 2 breeds will yield a faster growing bird than a purebred. The 2 I mentioned both have good body shape, and I've tried crosses of the full sized versions with good results, so the bantams, though smaller, I would think would have a similar body configuration. The Cornish gives that nice breast, the Brahmas have meaty legs, and are also broad, meaty birds.
Standard Cornish roo is a good choice for the terminal sire for a meat cross, I haven't done a lot with this yet, but from what I've read of other folks experiments, Cornish roo over pretty much any other heavy breed hen, will give you a pretty good meat bird.
There was a member raising bantams for meat, who was pleased with what he or she had, but I don't remember who that was, or what variety/varieties of bantams were being used.
