I Have a few Atlas 60' Reading and Northern coaches. they have the correct 2 wheel trucks. the only cars equipped with 3 wheel trucks are the pullman and office cars.
Not sure what the Pullman and office cars are. I haven't seen any of these sets that have those cars. I have the Milwaukee Atlas 60' set - and I think this was true for all the different railroads done in this line - the RPO and baggage have 6-wheel trucks. All the rest have 4-wheel trucks.