I am not familiar with the new Lionel Gons, but I have converted the Lionel trucks on GLA hoppers, PS5 Gons, and PS1 flatcars by removing the couplers and replacing the wheelsets with 2 rail wheelsets. I have found that Athearn Wheelsets work, as do Intermountain metal ones. On some trucks they are a sloppy fit, but can be tightened by squeezing the sideframes in slightly.
The lobster claw coupler mounting rivets have to be drilled out and the truck disassembly to cut some stuff off the bolster in some cases to allow the truck to swing with a Kadee coupler box mounted.
The advantage of using the existing truck is that the mounting works without modification. To use any other brand you probably have to build a new bolster on the car. And just replacing wheels is relatively cheap, and free if you have wheelsets in your parts stash. Also, there is usually not any adjustment required for coupler height.
the first one I did took over an hour, but once I learned how, I can do a pair in about 1/2 hour, including touching up the paint where cuts were made.