Your right about the radius geometry problem with varying truck sizes. I have not studied or worked on this issue much. But one idea that I've found has some merit, but I can't say in which specific loco-to-car arrangements, is to try longer shanked couplers as this will extend the range of motion. You may lose some of the closer coupling look, but at least the cars won't derail.

Privprac

Yes, the Bachmann decoders are dual mode. So the loco can run on either DC or DCC automatically.

Can anyone tell me if the Bachmann 8 pin plug 1Amp DCC decoders (#44915) will readily fit into all Bachmann (and other manufacturers) DCC ready N scale locos?

I recently purchased a 4-8-4 Northern with DCC onboard. I have a standard DC system and will be getting an E-Z Command system. The loco comes with 2 jumpers. When are they to be used? The instruction sheet simply indicates using them after you remove the decoder. Why do that if the loco runs in DC mode without removing the decoder?