DaywhitemtnsI understand that the model is a scaled-up version of the Uintah narrow gauge machine and thus no prototype exists for the mantua model.
IIRC that idea - that it's a scaled up narrow-gauge engine - came from a review in MR (or RMC?) when Mantua first brought out the engine 30+ years ago, but later was disputed, as apparently the model was based on (or at least "inspired by") a standard gauge engine. I can't recall for which railroad right now.
The October 1991 MR had a good cover story on making internal and external improvements to the 2-6-6-2 model.
Here is a side by side of my 2-6-6-2 and a AC-9.I bought the 2-6-6-2 because it looks cute on my layout next to my biggies, runs very nice, a bit noisy but the sound decoder covers the noise.I run it as a logger, 21 log cars and either a bobber or Drovers caboose. Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.