Thoughts on the "tender powered" engines.

I love the look of the C-57 as it is slim, long and very well detailed. I may have been easier to a direct drive motor which wouldn't take up much space and have fewer gears in the engine body, have the battery in the Tender and still be able to keep the slim lines. 

I think slim looking body is one of the main reasons for making tender driven engines. And there is the solution: to put the battery in the tender, and the motor in the engine body. Like (old) Edward! In many cases (not all) that would be the best solution, and the engine would actually pull the train.