My grandfather worked on # 65-97-66 Room 407 O.P.O Building in Manhattan, I believe. Similar numbers--but I haven't been able to find out what the project itself was. I wrote to the National Archives and they looked it up, but couldn't find that number. They said that it must've gone under a different number as well. (Maybe you've got the missing number?)
You should try emailing the National Archives. Try to get the address, too. My grandfather worked here in 1937, like your uncle. Maybe our relatives worked together for the WPA!