I recently visited a gentleman in California who had a separate 1 gauge layout, below his main layout. He indicated that the funny thing about 1 gauge and 5 rail track is that if you make standard 5 rail track using O and Standard gauge, that 1 gauge would run on it, as the distance between the outer rail of Standard and the far rail of O gauge was equal to 1 gauge track. He indicated that as long as the power pickup on the motor was wide enough to reach the center rail, the 1 gauge engine would run on the track.
Funny that you mention that. I have Gargraves 5 rail on my shelving so I can display both my std and 0 gauge pieces. When I put the Marklin on it, the flanges sit outside of the O gauge section allowing the Marklin to "ride" on the std gauge rails. I was thinking this might be an option as well as I know I can get the gargraves track. Also I have enough O gauge track, I could probably even take my current std track and graft the O gauge to it.
Now the wheels are turning, that's not always a good thing