"I'd rather not say what ship or when. I'd also rather not show the whole piece."
Probably a wise move, but just say "won't". It keeps us from wondering if we can ever pry it out of you:

Abourt twenty-six ships went down, and many of these were recovered and scrapped. Assuming you're wanting to date the stamp, and already know about the company; you might head in the direction of brass door locks which exist in numbers, and where some are dated. Other brass collectables also exist which can be dated. Many of these were made by the Detroit Ship Building Co. and bear the same stamp as yours.