Something to keep in mind: If you keep at this, and you never get to a point where you're satisfied because while the image is cleaner, the field blending makes the image look shitty, make sure to take a moment to decide whether you should do this project or not. The source you have has some major, major issues. Should this really be used a source for preservation purposes?
Hopefully you can work some magic, but always know when to stop and say, "This isn't the way to go."