I disassembled the negative ground, cleaned it up and reassembled it. It was pretty trashed. I scraped and brushed what I could and then sandpapered the tab lug down to brass, then cleaned the lug, nut, star lock washer and bolt. It wasn't shiney-new but it was a hell of a lot better than before. This is what I have now:
One thing I noticed was that there was originally something behind the welded-on back washer that sits 1/2" off the frame that the lug tab hits first. I could salvage one small piece but couldn't tell what it was. I actually looked like wood with small grooves but it must have obviously been rubber originally. It's gone now: How critical is that?
Then I took degreaser and went to work on the positive cable. I cleaned what I could as it got dark but it's a real mess and I'm sure I left a lot. Here's what I have now:
To clean this thing right I'm going to have to steam clean it, so I'll look into that.
The end result, you ask? Nothing. Nada. Zip. I think I may have gotten another half a cranking volt but not enough to start her...wah, wah, wah, wahhhhh...