To make this all look like it belongs I chased down the right parts. I got a black genuine E3D titan aero stepper motor, a black drive pulley, and black m3 x 7mm screws..



The way I hooked this up required no changes to marlin. There is a header next to each stepper driver socket that is a breakout for the Arduino pins that drive that socket. I connected this expansion board to the appropriate pins on the header next to the driver for the Y axis. And this whole mod is plug 'n play. Here is someone else's instructional video on making these connections:

https://www.youtube.com/watch?v=vIChqkEAuto&t

And here is my completed 2 motor Y axis..