Please keep up with this thread; I have a Focus with a munched valve seat too, and am considering sticking a Zetec in it. I've been trying to figure out what needs replacing and if it's worth it.
Ironically, I bought my car new and looked hard to find the SOHC engine because it gets 1 mpg better mileage than the Zetec. Until the valve seat falls into the cylinder, anyway. I haven't driven it enough to check the mileage since then, though I was considering adjusting the valves on that cylinder to never open, and pulling the plug wire to see what kind of mileage I'd get on three cylinders...
Thanks for putting in the time and trouble to keep us informed on your project.