I used to put up a 2 rail Christmas layout. I used the old Atlas 24" radius track. But I used an F3 diesel ABA set with body mounted couplers. Most of the time they didn't work. My passenger cars (18" cars) had truck mounted couplers and they worked fine. I found that if I used just the F3 A unit and the passenger cars it work fine.
However, if you can expand to 36" radius you will be better off. You may be able to use a Pacific type engine (with only 3 drivers rather than 4) it should work fine. I have a 2 rail Pacific (3 drivers with flanges) that I ran on 3 rail 072 (36" radius) track with no problems.
Let us know what happens.
Rick