DO NOT touch the overflow fitting or the "spacer" between the drain and the sink. Those a parts specific to that sink, not part of the drain assembly which will come with the new faucet. There are literally HUNDREDS of faucets which will work on the sink, adn they will ALL have a new drain assembly and pop-up unit..
Yessir! Thanks for the warning. My guess would be that I'd loosen that big nut on the bottom of the overflow, and that would allow me to remove and replace the drain and lower piping? How does the overflow feed into the drain pipe?