Came across this page... Steam Locomotive.com

I don't have documentation, but the East Germans implemented Boxpok drivers on some of their (excellent!) late Pacifics -- and there was some sort of quality issue with them in service.

If we are covering interesting cast drivers, we should surely mention Web-Spoke. These supposedly had most of the advantages of cast disc wheels, but at a lower cost and lighter unsprung mass.

There's at least one photograph in one of Staufer's books, I think Thoroughbreds, that shows a chassis with Boxpok, Scullin, and Web-Spoke driver pairs (!). I dimly recall somewhere that one of the 'ideas' was to use a disc main, to get the balance weighting correct without tinkering, and then use the lower-mass Web-Spoke centers on all the coupled wheels. If Voyce Glaze's balance were adopted (which only has 80lb or so overbalance in the main) all the drivers could be Web-Spoke without any perceived compromise.

There are other types of driver center, including the BFB types found in Europe and the centers used on the Victorian class R Hudsons (I forget what they're called, sorry!) which were stated to have the strength and balance advantages of a disc wheel but the lightness characteristic of a spoke wheel.