Russell era doctrine was not Adventist, but Age to Come, the American designation for British Literalism. Russell had known contacts with Second Adventists, that is Advent Christian Association and Life and Advent Union advocates. But he adopted the doctrines of the older Literalist belief system that developed in Britain starting in at least the late 17th Century.
Naturally, American 'Adventism' as a movement was a loosely defined outgrowth of British precedents. While he drew from an eclectic religious background for his unique particulars, his movement certainly was part of the American Adventist school of religious thought. Thanks for your passionate work.