Here is a camera small enough to mount in most N-Scale locomotives for that engineer view. It is the CM200 2.4ghz wireless camera - measures 38mm x 10mm x 10 mm. Shown on a Kato N-Scale F unit. Would be a tight fit in a GP/SD 7/9. It and a Receiver/DVR are available for about $50 , the camera alone less than half that. Requires 5Vdc at 200ma so a 9v battery would not work, four AAAA cells mounted in a trailing vehicle would or the camera and battery pack could possibly be mounted in an E unit. Al
I wanted to shorten and maybe downsize the 5vdc connector. Not so easy, the connector has circuitry inside that gives two seperate 3.3 vdc outputs with seperate grounds. I think one is for the camera and the other is for the 2.4 ghz transmitter. Al