Another happy customer. I originally put a Digitrax 123 into mine, with no problems. I swapped the long-hood headlight for a LED. Then, I was so disappointed by the silly arrangement of the cab-end light through the plastic "light pipe" that I removed it and put a LED right in the cab where it should have been in the first place.
Last year, I decided to go all out, and I had my LHS install sound. I have yet to remove the hood from the engine to see how they did it, because there's hardly any space there, but it sounds great and still runs very, very well.
You won't be disappointed by this engine. They are great.