Recently at my LHS, I noticed they had the new Bachmann fixed knuckle coupler on two axle trucks. I replaced an older Bachmann rapido style coupler/truck set with these new ones and they worked fine (they should - that's what they were made to do.) But I also have an older Con-Cor 125 Ton Gunderson double stack car that had rapido couplers. The rapido coupler popped out easily leaving the centering spring in place, and after popping out the Bachmann coupler, I reinstalled it in the Con-Cor truck and it worked perfectly. (The whole Bachmann replacement truck assembly won't fit correctly under the Gunderson car, but you can switch out the coupler and it works great.) If you have any Con-Cor products with the rapido-style coupler...you might want to try the Bachmann's as a $2.00 replacement. Granted, they're not as good as a MicroTrain or Accu-Mate, but for the price, they sure work well.

When I was into N scale, I used to replace the original trucks with Kadees(Well, thats what they were called back then).
The kits came with different bolster pins, for different manufacturers rolling stock(Or the original bolster pins could be used), but at $20.00 USD for a ten pack(this was twenty years or more ago), it did get quite expensive.