Ralph,
The basic process for switching an MTH engine between 3-rail and 2-rail running is to flip a switch and to remove the middle rail power pickups. Your biggest problem will be determining which 2-rail track your engine will run on; not all 2-rail track is the same. Since you don't mention it, I would guess your engine ran well on 3-rail track; you might not be so lucky on 2-rail track.
Chuck