The tab and slot couplers on the cars I run have plenty of clearance with respect to distance from the track. I've never had any problem with them running on regular O gauge tinplate track or switches. Below are some examples to give you some idea of the coupler/track clearances.
American Flyer
Bing
Dorfan
Fandor
Hafner
Lionel
Marx
Prewar
Postwar
Modern (Ameritrains)