The black roof is correct for SAL as-delivered 1937 cars (SAL B-8 and B-9 class).
If you are modeling a car repainted in the mid/late 1950s, the roof should probably be freight car brown. Photo evidence shows that the railroad repainted the entire carbody with a freight car brown ("BC Red") in that era.
BTW, all the cars were delivered with steel running boards.
On Rob Adams' Steam Freight Cars website there is a list of 1937 cars, made by Ed Hawkins and I think Ted Culotta as well, that covers the basic construction features of each SAL car series. You will find that spreadsheet very helpful. I have a half-dozen copies squirreled away around the house, and one buried in a jar in the back yard.
Also, I did a rather extensive article in the SCL Modeler magazine some years ago and can help you with painting and lettering depending on your era. If you want a copy of the article let me know.