What about a chassis like this?
The idea to build Lego trains capable of running on O gauge track is pretty appealing to me, I might even consider seeing if I can convert some of my Lego trains to O gauge. I see several advantages to it... The track will be closer to scale, will be much cheaper, and it means that my Lego trains can run on my O gauge track. Currently, I don't even have enough Lego track to sit all my trains on at once, let alone run anything.