I'd shorten the top logs, or put them on the bottom. Looks good.
One more suggestion: Next time weather the deck. I have not seen any pics of flats with painted decks. Most railroads used treated lumber, sometimes with creosote, sometimes not. You can use plain old earth tones to do this with. it doesn't have to be expensive Pulpwood flatcar decks got the crap kicked out of them pretty fast!