George,
PRR used the following National trucks based on a PRR typed list of truck classes and classes of cars to which applies. You can find the list at http://prr.railfan.net/freight/PRRFreightCarTrucks.html
National (no designation with plank) X29, X37, X37a
National (no designation plankless) X29, X37, X37a
National A-1 G26, G30
National B-1 X41, X41b
National C-1 G32, G33, G37, X43a
Rich Orr
