It may have a Lionel motor and possibly a 726 or 736 chassis, but one thing it's not is Lionel. The first Mikado Lionel ever made was by Lionel/MPC when they replaced the Berkshire's four wheel trailing truck with a two wheeled truck in 1983 for the Famous American Railroads series #4: Southern Railway.
Most likely scratchbuilt model by a fairly talented modeler, possibly using Walthers parts.
Rusty