It may help to do the opposite. That leaves a bit of the neck near the shoulder unresized which can help center the neck in the chamber and can mitigate any tendency you may have to extrude the neck further forward. If you decide to outside turn the necks, that may be the best way to load them afterward, at least for the first few times.
What would be ideal is if you could find one of the old Lee Manufacturing (the defunct predecessor of Lee Precision) Zero Error Lee Loaders in 270 Winchester. These tools have an inside neck reamer that uses the die as a journal to keep the reamers centered while the neck is likewise held in place. As a result, they thin the neck from the inside while keeping it very even in wall thickness for an inside reamer. This would solve your neck thickness without changing the taper in thickness that is supposed to be there.
What would be ideal is if you could find one of the old Lee Manufacturing (the defunct predecessor of Lee Precision) Zero Error Lee Loaders in 270 Winchester. These tools have an inside neck reamer that uses the die as a journal to keep the reamers centered while the neck is likewise held in place. As a result, they thin the neck from the inside while keeping it very even in wall thickness for an inside reamer. This would solve your neck thickness without changing the taper in thickness that is supposed to be there.