Ford doesn't have a service interval for the timing chains far as I know. And in fact, I only know of one case in which a timing broke and the cause was likely worn/bad guides or tensioners.
Having said that, I think replacing the chain guides is more important. I replaced my guides around 175k because I was nervous and heard a tick. They showed some wear, but actually had quite a bit of life left still. I think it wouldn't be a bad idea to replace the guides every 150-200k miles. I have read this is typically done on fleet vehicles which are driven 400k+ miles (think police and taxi service).
If you want to replace the chains and tensioners as the same time, it wouldn't be a bad idea. Just adds a bit of cost, but it's the same amount of labor.