Found C9ZA-3556 S used on the 69 Boss 302's I've got pictures of and all have the standard, normal clamps installed (all unrestored cars)
Also looked about 100 70 NJ cars and could not find a single example with anything but the one piece standard clamp as we normally see.
To support the idea that these are original you will need to find a number of other original examples before you'll get any ones attention unfortunately I didn't find anything to lend support
At this point I'm guessing that something took place sometime in the past with these springs - but just me at this point.
BTW if we read the last two numbers the way that is currently accepted your springs were stamped on April 5th - unfortunately we don't know what car they came from