Ever replace leaf springs ?

So let’s say they are beyond regular hand tools.
If an impact wrench will not break them loose with your pre-soak, the nuts could be split, the bolt cut off with a reciprocating saw or when there is room, cut off with a torch.

Do you have enough jack stands for both the car and axle? What about an impact wrench or a couple of breaker bars with extensions?

The front bolts on mine had corroded and bonded to the bushings themselves somehow. The nuts came off easily enough after 50+ years, but since the bolts had bonded with the bushing/sleeve on one side, I actually ended cutting the old leaf first with an angle grinder and dropping the rear end out, then going back and cutting the eye apart piece by piece...then the bushing itself, and finally the inner sleeve...all it all, it was about 2 hours work...that is the worst case scenario though....yours might well come out with little real effort. I will warn you though...the CJ pony springs probably wont last more than 5 years(from when they are first installed) before they start to sag...they are not great quality....most people recommend Eaton springs