Spiral Shocks

[Mr70]

That's my personal "i.e." reference after Heavy Duty that I believe Chevrolet really used in that situation back then.
Of the few heavy duty suspensions I have seen in person on any GM B-body,Buick-Olds-Pontiac-Chevrolet,all have had Budd frames.
I can't find it right now,but somewhere I have a internal product bulletin stating Chevrolet preferred to use that manufacturers frames when special heavy duty suspensions were requested before assembly.
It when on to say because Budd used a heavier gauge steel on it's one piece tunnel bottom & welded on channel rails then other similar frame manufacturers at that time,GM preferred to use them more in case of warranty issues.
I think Parish Pressed Steel later on adapted to this design as well..