@bob2 unless I'm mistaken, that conversion involved bolting a Williams 3R chassis and cylinder saddle under a Lobaugh boiler. It was a lucky coincidence that everything lined up.
I remember all the grousing from the two-rail guys about the Atlas 0-6-0. It was never good enough for them because they knew that deep down, it was fundamentally a hi-rail loco. Among other things, 3-rail locos must have a narrower chassis and/or a wider cylinder saddle to accommodate the wider driving wheel tires (traditionally about 0.215" vs. 0.145" or less for scale.) Going from Hi-rail to scale, you could cut down the wide tires, make new ones, or swap in 2-rail wheelsets. You would probably have to add washers or spacers between the back of the wheels and the frame to take up the slop and keep everything centered. Such a conversion requires a lot of skilled machine work, but it's doable.
Going the other way is very difficult or impossible. Even Joe Foehrkolb refused to do it. A loco born exclusively as a 2-rail model will start out with narrower wheel treads and a correspondingly wider frame. Even if you get the 0.215" treads with pizza cutter flanges to straddle that chassis and still fit within the gauge, you would have to redo the cylinder saddle, valve gear, etc. Major problems.
To the folks who keep mentioning the C&LS model: it's irrelelvant whether it sells for $2 or $2000. It's not operable on any hi-rail layout, and since it began life as a pure 2-rail model it can't be converted in situ to 3-rail. Perhaps you could bolt a Williams J chassis under the WM boiler, and some people would be happy with that. Personally I wouldn't, and I can't imagine that such a conversion would be cost effective. As I said before, it might as well not exist and doesn't affect the economics of an exclusively 3-rail production run, except that we shouldn't expect our 2-rail brethren to bolster the reservation count.
I'm starting to think that this big, rawboned, and handsome 4-8-4 could be a future Lionel Brass Hybrid riding on the N&W J or Reading T1 chassis. In either case, newly tooled driving wheels are a must!