Can you replace the trucks & couplers on older rolling stock with the new magnetic style that are on the newer cars?
There are many options for swaping trucks. Bachmann, Atlas, Microtrains, and BLMA all offer replacement trucks. Some are trucks only, some are talgo trucks (coupler mounted on the truck). With Bachmann, many of the brands may need the bolster hole reamed out to fit their cars as they use a screw mount bolster which is larger in diameter than most other brands.
http://www.spookshow.net/trucks/trucks.php