Your vise is a lot older than you think.
Dunlap line of tools started in the late 1920's. There is a good chance that vise is 75 years or older. Hope this helps some. By the way, an excellent stout vise. Don't part with it.
Your vise was made by Littlestown Hardware & Foundry. They were made for many retailers like the old S & H stamps company who would add there own name to it.
They were made in the 1960's & 1970's. Hope this helps.
Bob