Bluezone-
I'm not going to be able to answer your question, but I once had a set of rear spring made for my 1927 coupe from a local supplier called Eaton Springs. At the time I was impressed with the large number of original bule prints that they had on file going back into the early 1900. They have a web site
www.eatonsprings.com If you contact them, you will need to be ready to tell them the year and body style of the vehicle and number of leafs the spring has that you are in need of.
Herb-
When I restored my 28 Roadster I took the springs apart. I was surprised to find that,on the rear springs in particular, the ends of each leaf had worn a three sided box into the leaf surface that it was in contact with. These worn in box areas were restricting the spring leafs from sliding across each other during compression. They were just as you describe, stiff as a brick during ride motions. I corrected this condition by chamfering the ends of each leaf and grinding away the sides of the boxes that had been formed, do to wear over the years. While apart, I mannually re-cambered the main leafs in my bench wise. (Don't over do it).
On my current 1928 project, the vehicle had Delco Lovejoy lever action shock absorbers when I purchased it. I'm not sure what year these shocks were designed for, but each spring had the short 1928/1929 snubber leafs removed and a neat cast spacer installed at the U-clamps to fill the gap were the snubber springs had been removed. The installation also had cast spring to axle U-bolt lower clamp plates designed to accommodate the strap between the shock lever arm and clamp plates at all four locations. I've never seen shock absorbers on a 28 before and since I'm attempting to accomplish an authentic restoration, I'm planning on their removal unless I can find some documentation to validate their usage. I'm wondering if these shock absorbers were part of some other GM product at that point in time, but the fact that there are exact fit blocks added at the original snubber spring locations really bugs me. Anyone have any words of wisdom for me on this issue?