My Great-Grandfather on FOX TV

I was contacted by the art department of the FX TV show Damages, asking if they could use an illustration created by my great-grandfather about 100 years ago. It's a drawing of the New York Custom's House that appeared in Harper's Weekly. They wanted to enlarge it, and hang it on a wall of a judge's chamber behind Glenn Close. I guess they contacted me because I maintain a website dedicated to the artwork of my great-grandfather (www.ejmeeker.org). Unfortunately, I don't hold the rights to any of his work; it was all work-for-hire, mostly for the newspapers and magazines of the late 1800's. I was tempted to give them permission (not for the usage fee, but for my great-grandfather's memory), but thought better of it. I don't need any lawsuits for copyright infringement.
UPDATE: The FOX copyright clearance guy confirmed that Harper's still holds the rights to the drawing - so they used a photo of the building instead. Sorry, E.J.