Just remember that the reason those old wooden ladders could be built so light is that they were built of riven wood -- perfectly straight grained with no run-out. That makes a huge difference in the strength of a piece of wood.

If the ladder isn't plumb, the sides are in bending. And if it is plumb, it's hard to climb (dangerous).

If you wedge the rungs, make sure you place the wedges square to the length of the ladder, so you don't split the sides.