The reprint discovery engine for nineteenth-century periodicals archives would be a tool not unlike the Google Ngram Viewer, but focused on textual reprint and reference. This project would likely start by investigating a database like the Library of Congress’ “Chronicling America” collection, which is open and includes “an extensive application programming interface (API) which you can use to explore all of our data in many ways.”
I imagine the reprint discovery tool developing in two stages: