First, there doesn't seem to be any particular numbering system to differentiate the Leaders. In the United States it is popular to call the President "Number 42," but there was never any numbering system mentioned in the Legion stories. This was probably to keep the fans from realizing that the Legion had been around for more than 14 years....!
Here are the official leaders of the Silver & Bronze Age Legion, in chronological order:
Also, the election results for Dream Girl's victory in Legion (v2) #291 were not presented as a running tally, either. It was only after her election that she "broke tradition" and made the process an open vote, as shown in Legion (v2) #306 and Legion (v3) #12. It is also important to note that from these two election results we learn that only a clear majority of votes is necessary to win (and not a 2/3 majority or some other specific ratio). I have no idea what would have happened in a tie...would there be a re-vote, or would Legion advisor Marla (or later, Senior Advisors Costmic Boy and Lightning Lad) cast the deciding vote? We'll never know.
In these last two examples you can look at the Legionnaires' icons and figure out who voted for whom. For example, in Element Lad's first victory he was selected by nine Legionnaires: his write-in was started by Chameleon Boy, Brainiac 5, and Shrinking Violet, and that convinced Shadow Lass, Invisible Kid, Cosmic Boy, Saturn Girl, Lightning Lad, and Sun Boy to vote for him, too. Seven members voted for Dream Girl and six for Ultra Boy. Before these two elections you had to surmise on your own who voted for whom....unless a character was so bold as to announce their choice, as Shadow Lass did in Superboy/Legion # 226 (she voted for Superboy).
In contrast, Legion #36 was the first time that we get reactions of each Legionnaire to the Leader announcement, but not necessarily a clear knowledge as to who voted for whom. Let's look at the three pages of reactions.
Because we don't get to see the breakdown of which candidate got how many votes, it's impossible to tell for sure who else voted for whom, but with three candidates the magic number to win is nine. It seems fairly safe to guess then that the following members voted for Polar Boy: Sensor Girl, Quislet, Timber Wolf, Blok, Magnetic Kid, Shadow Lass, and the aforementioned Ultra Boy and Invisible Kid. Postulating that Polar Boy voted for himself (Ultra Boy did it when he was running) or that Element Lad voted for him, hat is a majority.
Outside of Legion continuity, the writers chose the Legion Leaders for the first ten terms or so; it was only with the election of Wildfire in 1977 that writer Paul Levitz allowed the Legion fans to write in and vote for their favorite character. This became the plot of Superboy/Legion #225, as Superboy received the most write-in votes, but Levitz balked at making him the actual Leader due to the nature of his membership. In the last few elections, the letter column usually announced the most vote getters. In Legion #36, this was the official fan-based tally:
By the way, one of those winning votes was mine, as I distinctly recall voting for Polar Boy in this election.