Although this part is offered, it will be quite a bump at the transition point due to a design flaw.
It really should be offset, like the GarGraves adapter pins.
You can make your own by starting with three "O" pins, and grind one end(to the half way point) of each 3/4 of the way around to match the diameter of the O-27 track pins/openings.
If you instead grind them to the center like the above Lionel pins, there will be a significant "bump" at the transition.
For an example of this "offset" method, look closely at the GarGraves "O" & O-27 adapter pins: