I'm aware of the trucks you mentioned. I have to have a lot of
them to put under my M&StL cars. The S2-A-O or 0 are 70 ton roller
bearing trucks. My friend is modeling a CGW Airslide

Clark, take a look at the Atlas 70 ton roller bearing truck, and
the venerable Athearn 70 ton roller bearing truck. They are both
quite similar in appearance to the Barber S-2 pictured in the
1961 Cyclopedia.