Wish I'd known sooner - I'm already committed for this weekend to Governors Island (another great national park, by the way). Somehow, I never seem to get to Steamtown when the weather is good - this weekend is supposed to be nice - enjoy!
You should call and see if they'll do a longer shop tour to let you set up cameras, etc. Might be too busy on a weekend. A couple of us went on a weekday a few years ago and they let us spend about an hour and a half in the shop. Tough light, but the most fascinating part of the place, in my opinion.
Also, not far from there (maybe a mile and a half) is the warehouse for Olde Good Things, an architectural salvage company based in Manhattan. Lots of fascinating NYC artifacts, and a huge yard filled with old gates, stone columns, etc. The folks who run it are very nice, despite apparently being a supposed cult (yes, really).
Great place for shooting lines of retired/stored locomotives, freight cars and equipment. I have shot there many times! Plus there is an active freight line with the Delaware-Lackawanna Railroad if you want to shoot some freight action. I would love to attend ... just a long drive from Colorado.