Question: I am trying to determine who "Rev. O. Everett" was who married my ancestors in Boston in 1788.
Answer: Your ancestors were married by the Rev. Oliver Everett who was pastor of the New South Church in Boston from 1782-92. The New South Church was a unitarian church located at Summer and Bedford Streets. The church itself existed between 1714-1866, and later merged with the New South Free Church. This later edifice stands at the southwest corner of Camden and Tremont Streets in Roxbury. Incidentally my own great-grandparents were married in a double wedding at the New South Free Church in 1874 by Rev. William P. Tilden.