Leaf Spring ID

Exactly. Back when I lived in North Jersey I went to a dealer that had a very complete set of parts books and took lots of notes on leaf spring part numbers. The parts book only give 'application' ie. Barracuda, special hardtop, v-8 except 383. The shop manuals provide the number of leaves, but don't cover all combinations. The Direct Connection/Mopar Performance bulletins and books provide snippets of info for both factory and 'P' parts.

Direct Connection / Mopar Performance sold (and I think still does sell) SS springs, Kit Car and Circle Track springs, and even got into the restoration game with some repop and some vaguely restoration products including springs.

Original leaf springs that I have seen use tapered ends on all leafs, and the corners are rounded. If that is universally true, then your set is some sort of aftermarket or rebuilt.

The P-part SS springs have a lot of initial (aka free) arch. The amount of arch will vary depending on the set: For a light car you would buy a set that came with less arch than a heavy car and maybe it had some other more subtle differences too. All versions had more free arch on the right. Spring rate was 160 #/in on both sides.
One of the Mopar Performance bulletins also give the minimum thickness for the main leaf and the first supporting spring. They also state the supporting springs extend to the middle of the front eye - like the ones you pictures.

Someplace I have a few p/n for other spring manufactures. IIRC Triangle's p/n start with 7, but I couldn't find the notes to verify. Of course since you're on the other side of the atlantic, its possible there are other p/n we don't come across in US-Canada models.

Even though these are aftermarket, going through the listings here will give you a good idea of what came from the factory - some are even cross referenced to the Chrysler p/n
http://www.stengelbros.net/Plymouth-Leaf-Springs_c_226.html
and
http://www.stengelbros.net/Dodge-Passenger-Car-Leaf-Springs_c_194.html