This is not my recommendation...but I remember seeing an HO engine, I think it was a PRR T1 but not at all sure, that was "articulated". Each set of drivers could pivot separately. The pivot points were close to or at the second set of cylinders. I believe also that this arrangement could be "made rigid" via screws for those in HO with layouts with very large curve radii. If you like PRR T1's, and who doesn't, this arrangement would permit operation on sharper curves, but I suspect that appearance would be abysmal on typical 3 rail Lionel 072. What this type of design WILL do is reduce the minimum radius on which these locomotives will run.
I am continually amazed by builders that announce 3 rail engines with very long rigid driving wheelbases, like the UP 4-12-2, and the ATSF 2-10-4's with 74" inch driving wheels. These engines are less acceptable of curvature than even a large articulated. Even a UP Big Boy has a shorter rigid wheelbase (although boiler overhang on curves is another potential problem).
