I've purchased some Lionel Ready to run sets and some additional rolling stock. The rolling stock I purchased after the set was much nicer in that the couplers were heavier, had spings and magnetic couplers. I went out and bought a bunch of the Lionel 6-14251 - Die-Cast Metal Sprung Trucks that they list in the catalog to Upgrade your existing rolling stock. They came with no instructions and the existing rolling stock appears to be press-fit riveted in instead of a screw and bolt. Does anybody have any experience with these? or have any suggestions? I know that he trucks are painted plastic so I didn't want to start digging around with a screw driver and scratch up the cars. Any help would be appreciated.