Ok to answer Andys question, I took off a leaf spring and measured it then applied the forumla to calculate it's spring rate. Spring rate with the AAL and without the overload(don't know how to factor in the overload) is almost 200in/lbs even (199.98768 to be exact) So it would appear that the marlin springs are a good candidate for swapping at 220in/lbs I think i'll order a set and just see how it goes will prolly stick the overload back on the pack as I don't think it hinders flex all that much and I do carry heavy loads from time to time.