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The 49ers have conducted eight known interviews in their quest to replace Jim Harbaugh, but those might not be the only candidates the organization is considering.

Defensive line coach Jim Tomsula, long considered a top in-house contender for the job, is not known to have sat down formally with CEO Jed York, general manager Trent Baalke and president Paraag Marathe. But, as one person close to the 49ers said, “His interview has taken place over eight years.”

The 49ers know Tomsula better than any of the other candidates. They likely have a strong opinion of exactly what to expect from Tomsula if he ended up as the permanent choice for the job he held as the interim coach for the final game of 2010 after Mike Singletary was fired.

Defensive coordinator Vic Fangio, whose defense ranked in the NFL’s top five in each of his four seasons on Harbaugh’s staff, was the first person to interview for the opening. According to a source, Fangio’s top choices to join him as lead assistants are Kyle Shanahan, recently released from his contract as offensive coordinator the Cleveland Browns, and 49ers secondary coach Ed Donatell as defensive coordinator.

[RELATED: Source: Fangio would target Shanahan, Donatell]

The 49ers are free to make a move at any point after satisfying the Rooney Rule with the interviews Thursday and Friday with strong minority candidates Teryl Austin, defensive coordinator of the Detroit Lions, and Todd Bowles, defensive coordinator of the Arizona Cardinals.

Former New York Jets coach Rex Ryan, considered the top candidate to land the Atlanta Falcons job, and Mike Shanahan join Tomsula, Fangio, Austin and Bowles as coaches who can be hired at any time. It is not know if the 49ers have reached out to any college coaches, who typically do not want any news of NFL candidacy leaking out due to the potential negative impact it could have in recruiting.

New England Patriots offensive coordinator Josh McDaniels and Seattle Seahawks defensive coordinator Dan Quinn, both of whom interviewed with the 49ers, could become available as early as today if their teams lose their playoff games.

New England plays the Baltimore Ravens, while the Seattle Seahawks face the Carolina Panthers. The 49ers could also show interest in Ravens offensive coordinator Gary Kubiak, whom the New York Jets and Chicago Bears have reportedly requested permission to interview. Kubiak said he would not interview for any jobs while the Ravens are in the midst of the playoffs.

Denver offensive coordinator Adam Gase is also considered a strong candidate. The Broncos play the Indianapolis Colts in the divisional round of the playoffs on Sunday.

Here’s the list of confirmed interviews for the 49ers head-coaching job:

Vic Fangio, 49ers defensive coordinator, interviewed Tuesday, Dec. 30
Dan Quinn, Seattle defensive coordinator, interviewed Tuesday, Dec. 30
Mike Shanahan, ex-Washington, Denver, L.A. Raiders coach, interviewed Thursday, Jan 1
Adam Gase, Denver offensive coordinator, interviewed Friday, Jan. 2
Josh McDaniels, New England offensive coordinator, interviewed Saturday, Jan. 3
Rex Ryan, ex-New York Jets coach, interviewed Sunday, Jan. 4
Teryl Austin, Detroit defensive coordinator, interviewed Thursday, Jan. 8
Todd Bowles, Arizona defensive coordinator, interviewed Friday, Jan. 9