Stock bumper and holes in the bed

[conoco]

I have looked online for an answer and have no luck. Anyone know what these holes in the side of the bed are originally for?

Also, is this rear bumper stock? I bought this truck from an 80 year old that is the only owner. Everything is stock other than the engine, which is stock but a 383. He used to use this truck to pull his race car and trailer to the track. I know these trucks were the work horses of there time and I could see this being an option. For purchase. I look like it though and all the lines are with my truck. To me it looks like it should be there. I just cant find info on it. The only thing I have left to do get it while is the paint and the side moldings. Thanks