I recently managed to make a single coal and iron ore train be completely full, and be quite a lot longer than the 320m station.
It did take a while, I started the game in 1850, and it took until 1895, but my train was holding around 190 units of coal and 240 units of iron ore. This was from 1 iron mine and 1 coal mine, whole trip was about 8 minutes with the fastest train I had at the time. Factory production was about 240/400 .. But because it couldn’t link and more cities to that cargo line, it wouldn’t grow further.
However, it looks very wrong when a train that’s too long for the station tries to enter and come out the other side, most of the front magically disappears, until it starts moving, then the back disappears off the platform until it catches up.
Strange.
But still, it can be done!
However, the goods trains supplying the cities were quite small 4-5 cars Max, and on average, about 60% full.