Sachs- Huret derailleur (re)installation Sachs - Huret derailleur installation

So the learning curve continues on the '85 Peugeot P-16. The main lessons are to take pictures and time getting each thing done.

I have the rear derailleur hung. There are two numbers stamped on the bracket - 24 &amp; 28. Since my large freewheel cog is 28 tooth, I assume there's some correlation.

Q: how do I know which notch the circular spring (which controls the cage/ jockey wheels) rests?

And second Q: the stock rear axle is held in place with a double nut (one piece - 2 nuts wide) on either end which includes a conical washer. This leaves about 3mm of thread showing inside the nut. There's about 5 mm of axle threaded into each side. Can I replace this factory piece with single of even double axle nuts (cone wrench thickness) so the axle &amp; nuts even out?
Here's an image of your derailleur showing the return spring attached to the slot furthest from the top of the cage
https://c1.staticflickr.com/9/8111/8602860708_0e4e4a50ef_b.jpg

To answer your second question, seems reasonable to replace the double nut on the outside of the fork end with a single nut.