Is this an option item?

[Toddmac]

Howdy gang,
I was looking at the rust collection under our 67 and I noticed something I haven't seen before. The truck has coil springs but coming from the back of the frame and running forward to the axle there are single leaf helper springs. Did all 67s have this or is this an option that is on here. I need to run the axle numbers too...it has a 12 bolt and it seems to have very steep gears to me. I was wondering if the thing is optioned out for heavy duty or some other kind of pulling package. Any ideas?

I forgot to add that the truck seems really high in the rear end and I always figured that is cause the bed it junk and missing alot of wood etc. That's the truck in my avatar.

Thanks! Todd