This only apples to AD versions. Not sure what you are working on, so this information might not apply to your vehicle.
I’m working on my 48 Chevy Panel/Bus. Mine had the planks but after being covered in rat poop and pee for who knows how long it was removed and burn 30yrs ago. I was more worried about the underside being exposed to the elements and what to cover it with to prevent rot. If regular plywood will work if covered, great. If not I have no problem buying marine plywood wood. joe