I had the CP Rail set with the SD40 and two dummies. Later I sold those and bought the IC SD40. I converted it to TMCC using maybe Digital Dynamics, can't remember. Lionel made replacement coil couplers for the SD40s but they would not center, I spent all this time including filling in with JB weld only to get mediocre performance.
I also had two frames for Santa Fe 2343 F3 diesels, the earlier ones with horizontal motors and a coil coupler on the nose, and made both dual powered with TMCC. Yes could pull, but also pulled alot of current. I used Rich Melvin's notes on TMCC "lashups" to control the pair.
I am predicting if you build the quad motor beast you will end up with something that has to be on its own transformer and still will not have cruise control.
I agree with some other peoples advice, just buy some engine that fills the bill - maybe find a K-Line EL Trainmaster that has TMCC (will have CC at the end). I do not know if K-Line made any with cruise control - I recently bought a K-Line NH EP5 and it does, and I have a K-Line 4-6-6T that has TMCC and K-Line's cruise control that still works.
Failing that, I like the previously mentioned idea of shell swapping with some other powered SD40.
I did a search on eBay, and plenty of EL SD40s pop up. But I did not see one Legacy engine. TMCC, yes, Legacy no. I tried MTH and boom boatloads of Erie Lackawana (sp?) engines with PS2 or PS3, maybe it time to try out DCS.
