I replaced the stock drivers with a set from a Con-Cor "Daylight" 4-8-4. Some early-generation ones would drop right into this S-2. However, in my case, I am using an early-generation Kato-built S-2 that had no bearing blocks on the drivers, while the "Daylight" was a later version that had them. I had to press all the drivers off the axles, slide off the bearing blocks, press the drivers back on, and requarter them all. It took a bit of doing, but not more than a couple of hours.