You did and if he wants to just replace the wheels he will need to find axles with the wire thin ends that fit in the old trucks. That being said, the old trucks have a lower bolster than the new ones from Atlas. How much modification do you do to use the new trucks? What I've done for yrs before Atlas started selling O scale trucks again was to plug to hole in the car bolster with rod plastic and drill a new hole for a 2-56 screw to hold Athearn or Weaver trucks. Those trucks match the old Atlas trucks for height in the bolster. I also put NWSL wheel sets in the new trucks. I do like your idea of the new Atlas trucks since they are metal along with the wheels which adds much needed weight down low for those old cars. Also Weaver now sells die cast metal trucks that could work with the Roco/Atlas cars but the bolster hole still needs modification.
Greg