In order for Milo Hamilton to famously state that Hank was "sittin' on 714", Aaron would have to hit his 714th career homerun. He ended the 1973 season with 713 homeruns after taking Jerry Reuss deep on the second-to-last day of the season.
Henry wasted no time in 1974 in tying The Babe, blasting his first homerun of the season on Opening Day in his first at-bat. In Riverfront Stadium on April 4, 1974 Hank Aaron tied Babe Ruth on the career homerun list.
Following the homerun, the game was stopped and Commissioner Kuhn and Vice President Gerald Ford (after a dispute with the groundscrew) stepped onto the field and presented Hank with an award for reaching the top of baseball's homerun list.
I have seen the video clip of the homerun in two places now. In MLBNetwork's Baseball Seasons: 1974 and in Ken Burn's 'Baseball'. Both featured the homerun, with Baseball Seasons filling out the surrounding at-bat and the post-homerun ceremony.
The BS: 1974 clip features the Milo Hamilton radio call, which is widely available in trading circles. The source of this color footage is not known despite my best efforts to narrow down between NBC, WLWT or WTCG.
As always, any help or information on the broadcast would be appreciated. As far as archiving goes, there could be two schools of thought on this game. First being, they stopped recording the game after Aaron hit his 714th during the first inning. The second, and what I think is more likely, is that the rest of the game was also recorded because each at-bat had the potential to be the record breaking 715th homerun. From there, however, whether this first inning footage was clipped and the rest destroyed, I do not know and only the people at MLBAM know how much of this broadcast they have.