Sorry tappet, but it is true. My dad in the 70's owned a Datsun 1600SSS. I think they are on your side the 510's. He needed to replace the front springs for some reason. Apparently the right one was a different colour (or had a coloured marking) from the left one to indicate which one must come on which side due to the one being a little stiffer to compensate for driver's weight.