I am in a similar space as Rusty. I keep my Gilbert Flyer stuff generally in its original state. Making these toys look like scale models requires a lot of skilled modeling beyond couplers, so I choose to honor their original look.
For everything else though I go with scale trucks (SHS, MTH, AM, Ace, S Scale America, etc) and couplers (Kadee 802/808 or my new favorite San Juan Car Company On3 Evolution).