for the first 20 years of its existence, the southern jumbo - along with its later "sister model", the natural finish sjn or country western, introduced in 1956 - possessed a round- or slope-shouldered design, which changed for both models to the more "modern" square-shouldered design (as debuted on the 1960-introduced hummingbird) in 1962. from 1949, in common with other gibson and their later sister line epiphone instruments of the 1960s, the bridge on the southern jumbo was of a "belly up" design, which changed to "belly down" in 1969, along with some modifications to the top bracing. in 1970, additional structural reinforcement to the top (the (in)famous double-x bracing) was introduced which, although it contributed to improved structural stability, had a deleterious effect on the tone. along with the country western, the sj was discontinued in 1978.