It is part of a circa 1940 Elgin headstock, missing the cast cover for the left side. They have some family resemblance to the Hardinge Brothers 1940 TR/ESM headstocks, but are quite different in design. This Elgin Tool Works operation was started by Franklin Hardinge in his Chicago oil burner factory (Hardinge Mfg. Co.) after he sold Hardinge Brothers around 1930 and Hardinge Brothers moved to Elmira, NY.
So, your headstock is sort of Hardinge, but not by Hardinge Brothers. The first picture shows a complete Elgin lathe (not mine) with a non-original Hardinge Brothers slide rest. The next pictures show an Elgin headstock and lever closer that I have.