Nice one! I don't see a stainless stamp, and carbon steel can pit like that; and so can stainless if it's exposed to something that will rust it. I'm inclined to say carbon steel, as it wasn't as prevalent in the Case lineup in 1970 as it is today. The Half Congress is a lot more practical. I'm getting a Camillus, most likely.
And Case Congress can be expensive! I was given a really banged-up 6488 (the big 4 1/4" one); and was hoping to find a little bit nicer one of about the same vintage. When it comes to older American made knives, I'm used to (usually 1960s and newer) Camillus, Schrade, and USA Bokers; none of which are that bad if I want a nice shelf queen to go with a banged up user (which used to be, and still are to a much lesser extent, cheap) I am looking at north of $150 for a decent one! Yikes!