Gentlemen,
Here are some semi-facts from my limited reference reference material.
Drawing from MRR mag, Nov. 1972, by Allen J. Brewster. The drawing showing the lumber door on the same end as the brake wheel and retainer, on car 5566, and two pics of different stock cars, showing the same position as the drawing. Instructions from two San Juan Car Co. car kits, long and short, calling the B end as the one with the brake wheel, retainer, and the lumber door.
I certainly would not call these references absolutely true facts. But two totally different references would point that way.
George