The Union Pacific HK-70-1 hoppers rode on 70-ton Barber S-2a trucks.  Notice the wedge shapes inside the bolster ends.  The newest HO version of this prototype is offered by Rapido.  I feel it is well proportioned, but falls short of proper wheel base.

I tried answering your question on Saturday but my post still hasn't showed up.

Brian Leppert
Tahoe Model Works
Carson City, NV

please visit www.resincarworks.com/tahoe.htm