Now O27 means O gauge, and the 27 indicates a 27" radius between the center rails. So there is no such animal as O27 54", or O27 72". Lionel and Marx O27 track back in the day were made by the same manufacturer.
No, it is not 27" dia. center to center. It's outer diameter at the ties.
They made large curves at 0-27 height and tube gauge... so Dr. Dolittle wins unless you're nit picking exact dia. but 50-ish 72-ish...yep.
Not made by the same specs nor assembled by some other mfg. All Marx is of a lighter gauge metal and plated differently.
There are two factors to 0-27 beyond the 27"O.D.. The rail code + tie height total, and pin diameter. The curve dia. is irrelevant to fitting two pieces of track, but code/hgt and pin dia. are a must (code is the height of a rail from "foot" to "rail head"/top (included is the "web"/upright)
Lionel 0-27 ties vary. Turned up edges like full-O in dark brown, brown, woodgrain. Rectangle (like Marx but slightly heavier gauge or harder steel) came in black, dark brown, brown, grey, black, unpainted (or clearcoated?)
Others might exist too.
Marx pins are 0-27 tube size. Blunt edges and thin ring for tube staking. Some are longer.
Lionels 0-27 are bullet tipped, with a fatter staking ring. Some brown tie track has hollow pins, noted by a seam on the pins length. These don't conduct well and if rusty can get red hot. The rust from the inside out too. I at least replace the center pin with a solid one as it does twice the electrcal work at most joints.
Note: If two pieces of track are aligned well and screwed in place, no pins is a possibility.