use something like a 1, or 1 1/2 ton. I have some that i pulled from an el camino on my Camaro right now and work good for basic moves. don't know the rate on them though. i had some from from a late 90's f150, they worked ok but were slightly big and would rub a little on my spring pocket because of the angle.
where are you at with the 3 1/2 tons? did you get them in and don't like them or are they not going in?
you are right, they are wayy to stiff for the front of the camaro. i would use stock front coils out fo a g-body or maybe a caddy or somthing heavier. maybe a 1 or 2 ton if you want it stiff, but its a unibody so i wouldnt try that.