O Scale Lionel ES44AC in 2-Rail.
This is only a sneak peak of the final result, this has been about 6 months or so in the making. I'm near being finished as I still have final wiring to clean up, handrails to extend, smoke unit to wire, etc. I'm having to press pause on this until Mid-October, currently packing up to move into a new house.
Here's some quick answers to questions you may have; once completed I'll post a video of it running and an answer more questions at that time.
Note, this was a very pricy project, right at $1000 by the time its all said and done, maybe a little more. I wanted to do it though; not sure I'd do it again due to cost. It took 2 Lionel ES44 Units, one powered one non-powered. The Powered Unit was dropped by a friends child and was unrepairable. I bought that unit and gutted parts I needed; Legacy Electronics were not reused. I bought the CSX Non-Powered Unit and transferred what I needed. The rest needed to name a few are:
-Wheels and Axles: NWSL 42", Electronics: ESU Loksound L Decoder, Lighting: various size LEDs from Tony's Trains (the Lionel LEDs were not prototypical colored at all), plus lots of others: wiring, speakers (Tang Band T1-1931S x 2), resistors, specialized tools, etc. etc., lots of trial and error. DCC could be a hobby of its own; this was my first go with it, I love it, far exceeds DCS/Legacy in my opinion.
When it was all put together is runs and sounds awesome. I can't say enough about the ESU Loksound L; why we have to deal with Legacy and DCS I don't know. The slow speed performance is also better than anything I've ever seen.