I was just reading about the Nissan factories. Unlike any other car model, the original Sunny (B10) was made in the Zama truck factory, which may explain why they last so long. Is it true the B10 had galvanized steel while the B110 did not?

I has been my understanding that Datsun did not have the capacity to add the 1000 line to it's body manufacturing plant at the time, so the job was sub-let to a "vendor" This was the Zama plant that you mentioned.

It is possible that at least some of these bodies were rust protected, particularly those that were destined for markets where salt would be used on icy roads.
I have seen a few pretty rusty Datsun 1000's, so it's probable that Aussie ones were not galvanised.

Many manufasturers have had, & still have, bodies made by outside suppliers.

I just happened upon a little white one of these (well a Sunny 1000, DeLuxe) sitting in a yard in my little town of Seto, Japan. It looks like it has been there since about 1973, 4 flat tyres that look like the originals, rust everywhere and the dash and rear parcel tray are covered in old stuffed animals. Next time i am near it i'll check the mileage, bet it is about 10,000. I also just found a Fairlady 2000 in behind a car yard (4 flat tyres too) in Hirajima.

There are quite a few 300ZX's around over grown with grass and 1 or 2 180SX's or big modern Nissans and Toyotas used as storage sheds or rubbish bins in gardens and empty land.