Straight out of the box, MTH's freight cars have the large AF-compatible claw couplers installed, as well as AF-compatible trucks with wheels. These will not work with "scale" track.
However, they are easy to remove. The couplers are truck-mounted, so just removing the screw from the bolster pin is all that is required to remove the coupler and truck. As you can see, the Kadee-compatible padding on the bottom of the car has all the proper holes pre-drilled (but not pre-tapped) for scale coupler installation.
My current standard is using the HO-scale Walthers ProtoMax couplers, which only line up with the center mounting hole, so I install those with one screw (from my parts box). The trucks are just a spare pair of scale trucks with scale wheels installed. Those are installed using the original MTH truck screw.