Slick 60's

Was recently looking at a friend of a friend's 62 f250 uni long bed which has some type of overload springs where the rear of the rear shackles attach to the frame. The owner is a bit of a purist in that he wants to leave everything factory stock and is thinking the overloads are probably aftermarket? I was guessing they are dealer add on's but don't really know, anyone know if overloads were a factory option, dealer add on or ?

Thanks.
Scott.

Not sure but I have a set of the overload brackets that clamp on the frame. Never seen them before either.