I have 1970 240. Did they come with a secondary fuel tank reservoir located inside the quarter trim and is connected to the fuel tank. If so was there one on just one side or both? Was this aftermarket or stock or dealer option?

That is an evaprative expansion tank, it is there to cause fuel smells inside the car-actually it is there to allow for fuel expansion and the condensation of vapors to keep them in the real gas tank.

Will

So original to the early 240s or not?

In the USA, yes. It was required for California emissions, so Nissan installed it in all of them. Through 6/71 production it was plastic, after that it was metal.

Not certain about the rest of the world.

Arne, FWIW my HS30 build date 12/70 does not have the evaporation tank. Can't be sure if this is the is the same for HS30's but I suspect so for the same era delivered to different RHD markets.