I've always wondered when that concrete was added to the bridge-- Triumph V has a pic showing the concrete in 1953 (it says), but I don't remember any mention in Rwy Age of when it was done. Maybe a closer look at their year-end lists of construction projects would show it.
There aren't that many published pics from before 1953, but it must have been just stone for a few decades.
You probably want to have Triumph V if you're interested in the NY Division, but aside from that pic it won't answer this question.
(Forgot about
http://historicaerials.com -- the 1947 pic there shows the concrete only on part of the bridge.)