N-Scale Couplers

[aliwall]

Hi Guys!
I have built up a reasonable collection of locos and rolling stock for my Denver & Rio Grande N-Scale layout, and find that the Rapido couplers on the majority of my stock are very unreliable, uncoupling frequently, especially on gradients. A few of my locos have knuckle couplers, which are much more reliable and look much better. I have managed to acquire replacement trucks with knuckle couplers for some goods wagons. However, trying to establish the right replacement couplers for my rapido equipped locos and Amtrack coaches is a nightmare! Does anybody have a simple way of identifying the right replacement kits - the choice seems huge!!

Aliwall
Pittenweem, Scotland.