check if this page still indexed,if you find the original content of a 404 error page with waymachmachine.org, for example, and duplicate that content can google detect as duplicate it if its no longer an active page?
check if this page still indexed,
copy some parts and google them using " "
if both returned no results, it should be fine to use,
never tested with an expired page within a working domain tho, just assuming
give it a try and see if it works, let us know