Thank you all very much for your replies!
I ended up using a combination of several replies: I used a "fine" grade 3M Roloc disc on a die grinder with the air set to only 15#, and Kroil as a polishing lube. The Roloc discs supposedly won't remove metal. Kroil is great for rust busting, and the combination of the two worked well. I finished off with a polishing rag and LPS-3. It now looks pretty, and I don't think I damaged the level.
I was thinking about what Gunner mentioned in his post above, about learning to live with rust. I think that's true; especially if you're in a rust-inducing environment like I am. I think it helps your sanity, though, if you draw a strict line, like: "no rust on measuring instruments or ways", or whatever is important to you. Then you can look at the motor case, or the gantry, or the whatever, and say, "Yeah, it looks like hell, but man, my (insert your favorite here) is clean as a whistle." Ridiculous, but what the heck. It's kind of like remodelling your house, where you don't tear up everything at once. Keep at least 1 or 2 rooms untouched so you have someplace to go to regain your sanity.
By the way, thank you for mentioning "Evaporust". It looked interesting, and I've ordered a quart to try.
Take care, and thanks again for the help!
Dave