It’s always sad when well-meaning people embark on a doomed effort. Current attempts at breed preservation are a good example.
Breed preservation is a very simple task. The goal is to take the surviving remnant of an old breed and maintain it so that it retains whatever fraction of its genetic diversity still remains. This is fairly easy to do with chickens, which are reasonably inexpensive to keep in the required numbers. Basically, the technique is to keep several hundred individuals and do random matings, with no culling and no attempt at selective breeding. This can maintain the breed, unchanged, indefinitely. That’s what preservation is all about.