If you mean one loop of track, with one conventional loco and one Legacy loco, and have them both go around the loop AT THE SAME TIME, that is gonna be difficult. You would have to cycle the power until the conventional engine is running forward, then try to get the Legacy up to speed. Easily solved by having a siding and park the one you don't won't running on the siding, and maybe a switch to cut the power if the conv is on there. Or just use the Hand-Of-God to remove the conventional.
Keep in mind you will also need a Lionel command base and a controller. I have the blue Command Base and blue CAB1L, there's the higher dollar CAB2 and not sure what its base is called. The original 1990's CAB1 is gray as is the original PowerMaster and Command Base.
