One thing I've never seen in 3-rail 0 is a high-sided ore car. Ore cars are small because ore, specifically iron ore, is very dense. When the iron mines started shipping ore in the form of taconite, a low-grade ore processed into pellets, ore cars had to get bigger because taconite is less dense than unprocessed high-grade ore. So, many iron ore cars were fitted with upward extensions on the sides, sort of like the extensions that turn regular hoppers into chip cars. Newer cars were built with bigger bays to handle taconite. I haven't seen any 3-rail 0 scale cars that represent older style cars with extensions.
Here's an ore car that's been modified for lighter-weight ore. This one is pretty crude-looking. The DM&IR and the Milwaukee Road, among others, modified whole fleets of ore cars on an assembly-line basis and those cars look much better.
