Thank you very much for your reply! (I was away from my computer yesterday, so am late in thanking you!)
I am down in south Texas. There is a photo in a 1943 issue of Oil & Gas Journal that shows one of these covered hoppers at a petroleum refinery in Corpus Christi, Texas. So they did come to south Texas! It was carrying catalyst for the fluid catalytic cracking unit at the refinery. My I&I model has the wood runningboards and is painted in accordance with Jim's painting instructions for the car number that was factory painted on it. I had looked in vain for prototype photos of these cars (only found one of the N-31 test car).