Bedside toolbox on a 64 GMC?

[Americanrider]

I was deep in one of the local junkyards today and spotted a 64 GMC Custom with good tires on it. I went over to take a closer look at the tires and saw it had a small bedside toolbox on the passenger side. It was in the same location as the 67-72 trucks (Foward of the wheel well on the right side). Is this something rare or a dealer add-on? It was raining heavy and I was not packing a camera, Sorry This truck has a 305 V6 & Auto trans, custom cab trim was once on it but gone now.