The difference in gauge is not a problem as proved by the many of us who have used Sn3 track in hidden sections, fiddle yards etc.
However, there is a critical relationship between gauge, back-to-back, over check rails, and check to opposite rail which if not compatible will cause running issues. A proper study and comparison of the o14 and Sn3 standards is probably required. That said I know some have successfully used Shinohara Sn3 points in fiddle yards.
John
