Dual rear suspension?

[Stepside65]

Finally got a good look under my new truck and noticed something i've never seen before. The truck had both coil springs and what looked like helper leafs. The trailing arms also had what looked like a reinforcement plate acrossed the bottom. Is that standard on a C20? I also have a heavy duty bumper that looks like it was built for towing heavy trailers. Was there a camper special option back in 63? The more I look at this truck the more it intrigues me.