Consider using Marx O-27(34) in the mix too.
You may need/want to use easements to get the inside(smaller circle) track away from the outside track approaching and leaving a turn to avoid the overhang from hitting equipment on the adjacent track. O27(72)-O27-O27(72), O27(54)-O27-O27(54), O27(72)-O27(34)-O27(72), or O27(54)-O27(34)-O27(54) as examples.