I realise that this is an very old post, but since this is a problem where many a M-880 owner runs into, i'd like to share my 2 cents...
To me it seems that there is nowhere nothing written about the spec's for these springs.
but spring basics says that to work at it's optimum, the spring shackles has to have a "certain" angle.
that angle determines the amount of travel upwards and downwards.
and if you then have a look at the situation at our Dodge's front springs, you see that the position, which I think that the springs had when they left the factory, is slightly "U" shaped instead of flat or "n" shaped.
I also take into account that the Engeneers at Chrysler have thought at a little driver and passenger confort, so the springs were intentionally made a little "weak" so to not rattle out the GI's false teeth..., and Time did the rest... because with that heavy cast iron engine leaning on it for more then 25 years, you'll see the results!
Almost any Dodge (sure the M-880 series) that i have seen has it's front spring leaves in the flat or "n" position.
I also like to mention, have a look at the spring shackles when your springs are in the above mentioned positions, they just don't have much "travel" left in this position, can you imagine how it can be with a pair of proper spring packs installed?
I'm sure it will benefit the steering and handling!
well, i hope this helps?