I would listen to BOB2 about this, he's attempted it before. I believe that last time, he just bolted the mechanism from a Williams 3-rail Mikado under a Lobaugh boiler.
I admit, I don't understand... Joe Foehrkolb (?sp) converts 3-rail steam locos to 2-rail all day long. Why is going in the other direction so difficult? Not only these proposed Berkshire conversions, but IIRC the Atlas 0-6-0 was shunned by the hard core 2-rail crowd for being "a 3-rail loco at heart." On that loco, all drivers were flanged. As a switcher, there were no issues of lead- and trailing trucks.
Is it because the driving wheel treads of a native 2-rail loco are prototypically narrower (and presumably its frame is thicker/wider), making it impossible to achieve sufficient lateral motion? Removing the flanges from the center drivers is an obvious mod (and even some 2-railers do this when they're challenged for space.) So what makes going from 2-rail to 3-rail so tough??
