This engine is definitely proto scale 3/2 convertible. Why not buy the 2-rail version with fixed pilot? It looks like there are still some available ( 22-20593-2 , 22-20594-2, 22-20595-2, 22-20596-2, 22-20597-2 . You will not need to do anything except run it.
Here is mine (2-20597-2). I left the 2-rail wheels on and run it on my 3-rail track. My latest video explains everything you need to know about MTH proto scale 3/2 engines. Click here -> MTH SD60e
Rich