cross sill - the support of the bed floor - sounds possible, tho I don't recall them on any of my 60's trucks - but then I think I recall less every day maybe my brain is full?
"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir "When we tug a single thing on an old truck, we find it falls off" ~ me Some TF series details & TF heater pics
maybe my brain is full?