I goofed - Got a Shelf Queen - How do I light her up?

I wouldn't attempt the DC. What I would do is change the wiring. It wouldn't be hard to do or put back.

No. Old-fashioned open-frame motors are also called "universal motors" because they will run on either AC or DC. You will need to disconnect the motor and e-unit entirely if you just want to light the train.

Here's another idea don't power the rails and put some DC led's in it as a temp thing ( use a glue gun or something like that so you can later remove the glue) and run your wires out of sight to it. 

the  lionel 752w (m10000) should have an e unit disable switch on the power truck behind the wheels. unless it has been removed which is common because as i found out from experience the lever will "fall outta gear" while running which is a pain if the train is in a tunnel or hard to reach spot on the layout

E-unit switch not found, otherwise this would be a no-brainer. For now, I just put a piece of electrical tape on the center rail under under the motor pickups.