The way I'm reading it you're talking about making a filled shell stock again? If so, Brookville repops the stock configuration, so two choices. You can contact them and see if they've got some scrap ones that didn't get punched right, say at the lower end, but that the top is salvagable and can cut a "patch panel" for you, or buy one of their complete units and sell what you've got (more likely what they'd urge you to do).

Plan B; Bazillions of these have been cut out over the years, but most likely thrown away. However, car guys tend to be packrats so you might try runnin an ad in www.fordbarn.com and see if anyone has the portion of a shell you're looking for.