1.66:1 is a weird beast. You can either do it letterboxed, and have black bars all the way around on a 16:9 TV but look right on a 4:3, or you can pillarbox the sides and fit it in a 1.78:1 frame for 16:9 TVs, meaning that on a 4:3 with no overscan, there will be black bars all the way around.
There's not really a good way to do it. Take a look at the Ultimate Editions of the early Bond films (like, the first 3) to see how they handled 1.66:1 in a 1.78:1 frame.