I wonder if you ever saw a wagon spring clock. There are few ways to power a clock and printing leaf springs outta pla and stacking them may give you enough power for a nice desk or mantle clock. I have seen these wagon springs even made from wood. The photo below is a complex metal setup, but it doesnt have to be this complex. And I dont think you will need the cantilever system. You make your spring, then attach a cord to them and wind up that cord on the drum. You could anchor the spring in the center and have 2 cords going to the drum, One from each side of the spring. However getting past a 36 hour clock might be the issue. You would have to tinker some.
Just some food for thought.