Dave Lawler asked:
"What was the purpose for the stake pockets(?) on the outside of the side boards?"
To hold stakes for loads taller than the sides of the gon. These are a common feature of period wood and composite gons. Here's a builder's photo of a PRR Class GRA with stake pockets:
Some later steel gons had collapsible stake pockets on the inside of the sides. The Proto 2000 52 ft 6 in gon is an example.