Well, you'll have to replace the couplers as the MTH ones will fry the Lionel coupler triacs, too low of an impedance.
If the MTH locomotive was a PS/2 unit, all the lights are 6V bulbs except the markers, they're two red or green LED's in series.
As for RailSounds, I'd just shop on the Lionel site for a suitable articulated RS4 board.
Likely the crew talk won't match the cab number unless yours is #4276, but Lionel has a RS5 board in stock that will drop into the EOB motherboard.
