In my experience YJ leafs are about a little shy of 100lb/in,,, a good referance for comparison of different trucks is a Rancho catalog, they list their spring rates. The problem though is that that guestimate of a spring rate is is just that, leaf springs tend to have variable rate.
damping constant is in units of force/speed, (FYI)... Dont know the rancho shock constants off hand, but dont forget, a lot of modern shocks are also variable damping rate.
If you dont mind, tell us what you are trying to do, maybe we can help,
In my experience, the theoretical engineering equations only work well when the right assumptions are made. And it is VERY difficult to make accurate assumptions about real world vehicles(ie: how friction in the spring bushings effects spring rate, and damping rate). They do work well, though on a slinky with a fishing weight on the end.
Just one man's opinion.
Good luck with the calculator.