changing couplers

Yes, it is possible. Generally, all you will need are some Kadees--very often, you can simply replace the old horn-hook coupler with the new ones. If they don't fit for some reason, you can get various adapters and widgets to help the process--but very often just opening up the old coupler box, tossing the horn-hook and putting the Kadee in its place, and then either snapping (ideally) or gluing (CAREFULLY) the coupler box back in place, will do the trick.
 
Listening to the conversation, I have to add that I have a Lionel SP GS-4 and the loco and tender were backdated to a GS-2 configuration. It is one beautifully detailed and accurate loco! Sure, its not worth much to a Lionel collector, but I couldn't be happier with the results. So go ahead and change out the couplers and start enjoying your Lionel loco. We are into this hobby for the joy of trains and not for the resale value of our investments!
 
ed acosta said:
Sure, its not worth much to a Lionel collector....

Just doing our part to make sure the collector's "investment" is a goodn':thumb:

It shouldn't be too hard to modify it, probably only need a pad built up on the tender to set it at the right height.