Without looking at other MTH units. The Russian Decapod is a 3/2 offering. Note that left and right wheels are isolated/insulated from each other, necessary for 2 rail operation. I guess the three rail flange is assumed to operate on two rail. There are no smaller flanged wheel sets, unless you order a two rail model. Conversion involves removing the third rail pick-ups from the tender. There is also a 3/2 switch on the tender.
Tender truck insulated side frame and wheel insulation pictured.
Three rail pick-up and axle pick-up, long copper strips that ride on the axles.
Removal of the third rail pick-up. Reassemble after the pick-up roller is removed. Front truck on the tender is left rail. Rear truck on the tender is right rail. Note that the axles are/or should be, properly installed for two wheel/axle pick-up Again note the insulation bushings, wheel sets pictured.
Three/two switch and another switch to reverse polarity. I assume this is a conversion to two rail DC.
My observation, I'm a three rail operator. Best to contact someone who has done a two rail conversion with one of these locomotives/units. Three rail Wheel flanges would be a consideration, as I mentioned the decapod has larger three rail flanges, not both.
All other axles/wheel sets on the locomotive are insulated left/right. Checked with an ohm meter.