I think I am right in saying that the LMS 8F would not have carried the maroon livery. This was for passenger locos only and freight engines were painted black. However, I am happy to be corrected on this point! There is nothing wrong with a 'what if' livery. For example, Rapido did this recently with their 15xx pannier tank, producing a variant in post war 'G W R' livery which they never wore, being introduced after nationalisation.