Factory 1/2 ton dually???

[Wulfaz]

I recently was given a 1970 Chevy pickup from a family member. I am trying to figure out exactly what I now have. It has a 350 motor and is a dually (with the extra wheels going under the bed, Not sticking out the side of the truck). But according to the VIN number it is a half ton. It also has a gooseneck ball in the bed.

Did chevy make a factory 1/2 dually or did somebody do this aftermarket? Also would a 1/2 ton frame even be able to handle a gooseneck trailer?