This shell is an accurate representation of the NRE 3GS21B in N Scale. To complete it you will need the parts outlined in this spreadsheet: Google Docs BOM
You will need to make minor modifications to the frame of an atlas B23-7 with blomberg trucks to make this fit. You will need to remove the bridge that goes over the motor.
Etchings for handrails and grilles are available at cescalemodels.com