Minor victories: I was able to crack the nut with the cold chisel/drill technique, and finally have it off. I do not think I can save these threads with a simple M20 die chase:
So I'm in the market for a new bar. I've already contacted Gwynn Lewis (where I purchased the bushings) to see if they have a reconditioned one available (awaiting reply) and will also contact the previously mentioned site here in Germany.
To answer the question re: the aftermarket nut... yes. A set of nuts came with the bushings, and in my ignorance, I believed the "brand new, virgin" nut would be better than the 22 year old one.
Other note for the record, in case some other rookie comes along doing research before he gets in to this: If you are holding the cold chisel while also cupping the cup washer so that it doesn't "ring", when the chisel cuts through, you run the risk of pinching the meaty part of your hand between the chisel and the washer. When this happens, it's helpful to have a band aid near by, to keep you from getting too much blood on the washer. Just a helpful tip.