I'd say just trash them. There are plenty of replacement headlights out there from suppliers like 5.0 Resto that will be better than the factory originals as far as being resistant to turning yellow and milky. I like the ultra clear headlights. They are similar to the 1994-1998 Cobras. However, if you have to keep the old ones like me, try an obital buffer with some compound. It won't get rid of the yellow, but it will be clear and not so milky. Touch it up with some Eagle One trim restore.