You said you have Bachmann rolling stock in both 1:24 and 1:20.3? Is it possible that you meant 1:22.5 which is the scale of Bachmann's regular rolling stock and has couplers that are truck mounted the same level as LGB and Delton? The reason I ask this is that Fn3 (1:20.3) Spectrum cars are scaled quite a bit larger and have body mounted couplers that are at a different height! Bachmann makes a coupler that is offset so that a body mounted coupler will mate at the same height as a truck mounted one. If that is your problem then this might be your solution.