I looked at some online auto parts stores. I compared some common parts for the 2500 and single wheeled 3500. Except for the springs, all parts I looked at were the same part #s, axles, hubs, brakes, U-joints, etc. Even the wheels are the same. They both have front coils and use the same springs.
Both the 3500 and 2500 before '14 have leaves on the rear. I think they put coils on the 2500 after that. My '08 2500 also has air bags and I can bring it up the 3500 capacity with an air hose. They're readily available for all years and both leaf and coil springs.
