I pulled and pushed on the couplers. With 2 rail, it is very easy to derail a car pushing on the top. I think this answers the question of sufficient coupler swing. The rest of it with a train probably is going to behave about the same as with 3 rail couplers.
Generally with stuff I have worked with, if the trucks roll OK, body mount couplers tend to NOT stringline, or derail cars on curves as readily as talgo (truck mounted) couplers.