Besides the screw holes you would have to cut the rounded end off the A unit frame. Not sure about the couplers on the front end, if you can remove or re-locate the coupler. I have not worked much on MTH engines.
I have swapped or turned around (180 degrees)an SD-45 shell on a Williams engine. Just needed to match up the shell and drill new holes in the frame. Williams engines have a universal truck assembly and swapping couplers is not difficult.
Lee Fritz