It looks more and more like an ex-NGNGRR tank.
Compare your photos at:
to the top photo at:
(Copy and paste a line at a time if that long URL is wrapped)
The tank cars behind the locomotive have low domes like the one you
I no longer have the NCNGRR book by Best but I photocopied the tank
which I can't find now!
I haven't seen that low-style dome anywhere else.