If aftermarket springs are a guideline, 1955-71 springs should be the same. I would check with a traditional automotive spring shop for eye-to-eye center lengths, leaf count and individual leaf thickness.
There were military stacks and civilian stacks. Also, the M38A1 military frames had the anchor at the front of the front springs, shackle to the rear of the front springs. My '55 CJ-5 was also this design—stock. These must have been M38A1 frames on the earliest CJ-5 assemblies.
Spring rate can differ per spring set, and leaf count is often nebulous. A spring shop uses leaf count, leaf length and the individual spring leaf rates as a guide. Leaf thickness, length and the spring leaf material will create different load rates.
I have always installed either freshened or new springs on these early Jeep models. The OE springs tend to torque sag to the left side of the vehicle over time. If you do install used springs, you will likely see a sag to the driver's side unless the springs have been swapped side-to-side. Springs are "perishable", and they lose tensile over time. At the least, you might consider having the springs "rebuilt", which consists of disassembly, cleaning, shaping and re-heat treatment.