Thank you very much for the comments, that has confirmed what I more or less thinking. I have looked for images of these wagons and of those I have found, none are finished in a company identity. Just a generic dark finish, so I shall do the same.
Re the 'lightly distressed' finish....I thought it was just sloppy mould making, I didn't think the finish was intended to be that bad! I have actually smoothed the solebars to try to improve the appearance.
Very many thanks, stay well.