In the early 1900s mission presidents addressed the general conference of the Church.
At least twice per year during his tenure (except, perhaps, 1901) Mission President Duffin took the two-day train trip from Kansas to Utah for the (usually) three-day conference. A typical trip lasted four to six weeks. In addition to the general conference, Duffin met publically and privately with various general authorities and other mission presidents to report on and plan missionary efforts. He also visited his family and tended to personal business.
As others have noted elsewhere, General Conference in the early 1900s involved more “conferring” than it now does. The Conference Reports note motions, votes, dissents, and other elements of an interactive meeting. Although the First Presidency, Quorum of the Twelve, and Seven Presidents of the Seventy took most of the time, various others also spoke. 
I discern no pattern to when or in which venue the Mission Presidents spoke and have not analyzed the content of their talks. After his release as mission president, Duffin spoke in three additional conferences (but only outdoors or in the Assembly Hall).
Below are graphs showing the relative percentages of each Conference Report occupied by speakers from various organizations. The first graph shows percentages for only the Tabernacle sessions; the second shows all sessions. 
The “Southwestern States Mission” series uses the diaries of six missionaries who served in eastern Texas around 1900 to illustrate aspects of Mormon material culture, lived religion, and social History. The missionaries are Mission President Duffin and Elders Brooks, Clark, Folkman, Forsha, and Jones. The series is inspired by Ardis Parshall’s serial posting of the missionary diary of Willard Larson Jones at Keepapitchinin. Previous installment here.
 Speakers included mission presidents, stake presidents, assistant church historians, bishops, the Presiding Patriarch, temple presidents, and a handful of others whose ecclesiastical office (if any) I have not identified. If I have counted correctly, 140 individuals addressed sessions of the general conference held in the Tabernacle, Assembly Hall, or on the temple grounds, from the 1897 October meeting to the 1909 April meeting, inclusive. In this time span three sisters addressed outdoor overflow sessions.
 The “organizations” are First Presidency (3 members), Quorum of the Twelve Apostles (12), Seven Presidents of the Seventy (7), Mission Presidents, Stake Presidents, and Other. The last three are not “organizations,” per se. There were about five US missions (with shifting boundaries, names, and leadership) and five non-US missions represented and, by 1909, about fifty stakes.
The graphs are in “first draft” condition. They are based on quick estimates of the column length of each talk with organization membership as of the sustaining of officers in each respective conference. I excluded the sustaining of officers and the report from the Sunday School Conference. In some of the Conference Reports the outdoor talks are only summarized and are, therefore, not included in the totals.
My apologies to extremely color-sensitive or color-insensitive readers; I fiddled with the color scheme for a couple of hours before saying, “It’s just a blog post,” and surrendering my effort to make something clear, pleasant, and unambiguous.