I've skimmed through the workprint a little bit, and so far my #1 suggestion is this:

Make sure you replace ALL the letterboxing! In skimming through, I noticed that the letterbox bars alternate between being black (as it should be) and various shades of dark-to-less-dark gray depending on the shot. This doesn't really matter for a workprint, but for the final product it needs to be consistently black, otherwise it's going to be incredibly distracting.

Other than that, I watched the Vader unmasking scene, and it's not that jarring. You can tell the non-GKAR shots are clearer, but it could be much, much worse.