I look up Estwing quite often on ebay but mostly for the brick hammers
I have seen several of these knives over the years and even clicked on them but sorry to say I have never paid much attention to them or know anything about them
I would email Estwing on their website and see if they have any answers for you
I had an inquiry a few years back about an old leather handled brick hammer that I had bought and they gave me a rather good answer but it did take a few days before they got back with me
Looks like it will be a good project though