Also, a double SD-40. Essentially, what the modder is doing is creating a "tender" for the lead unit, that just happens to be the same engine as the lead. There isn't any reason why one cannot mix-n-match to have a lead unit different from its tender, but nobody has yet made any such consists. All of this is done outside of the game, though; you have to create a unique engine mod and load it into the game (i.e. with the double GP-7 mod, when you go to buy an engine you'll have two different engines, one single engine and one double engine). You can't buy two single engines and then "team them up" on a train.
More complex things, such as flipping the tender unit to face backwards (like I did for my SD-40s), can be done, but this requires higher-order modding skillz.
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