I received a call later than morning - the seller indicated that I was the first email (pays to get up early!), verified that the $20 included the rule and other parts (always a good idea since the seller could have just been selling the protractor part of the square) and headed out to pick it up. The guy selling indicated that he had purchased it around 15 years ago for $100 but now didn't have any need for it. He also told me that he was surprised at all the calls he had received as he didn't think there was much need for something like this these days. I told him that I wanted it to use for woodworking which also surprised him (he didn't see any reason to have increments in 64ths for something like wood).
Anyway, I've always wanted a 24" length Starrett Combination Square and that's what I got, a number 16 rule with square, protractor and center - this one was wrapped in oil-soaked rags with only a hint of rust in a couple of places - there is some grime that needs to be cleaned up but otherwise it's not bad at all. It's also missing the marking pin but fortunately I have one from another that I an add to make this one complete.
In all a good day of rust hunting - I'm naming this one "Spivey" after a former owner.