In looking up some information on the National Invitational Hockey Tournament I came across the following information in the 12 February 1974 issue of TIHN (The Intercollegiate Hockey Newsletter):

The information below has been extracted from the 1974 NCAA Ice Hockey Championship Handbook
The National Collegiate Ice Hockey Championship provides for a single-elimination tournament comprised of two teams selected from the East and two from the West. The NCAA Ice Hockey Rules and Tournament Committee will seed the teams prior to the start of the tournament. In even numbered years, East #1 will meet West #2 on Thursday and Friday's game will match West #1 and East #2. In odd-numbered years, Thursday's opener will be West #1 against East #2, and East #1 will play West #2 on Friday.
The NCAA Ice Hockey Rules and Tournament Committee shall make the final selections for the Championship. The chairman of that Committee will appoint an eastern and western advisory committee no later than January 15. Each advisory committee shall consist of a chairman, appointed from among the members of the Rules and Tournament Committee, and two members. There will also be two alternates designated to replace one of the three members should his team be under consideration for selection.
The chairman of each advisory committee will contact all NCAA member institutions in his area which sponsor intercollegiate ice hockey to determine which colleges would compete in the championship if selected. If a college states that it will not compete, or if no reply is received, that institution will no longer be considered by the advisory committee.
Each advisory committee shall rank the top five teams in its area (without an NCAA playoff) and submit its recommendation to the Rules and Tournament Committee not later than Friday, March 8. The final selection will then be made on a conference call among the members of the Rules and Tournament Committee not later than Sunday, March 10. Announcement of the four teams selected will be made by the NCAA national office.

The following principles are adhered to by the advisory committees:
1. All NCAA members which sponsor intercollegiate ice hockey will be considered.
2. The winner of the ECAC Tournament shall be one of the teams representing the East.
3 The winners of the two sectional tournaments in the western region (WCHA Playoffs) should not be regarded as automatic selections, but the playoff games should be considered in the selection process.
4. A minimum of 15 games against college opponents should be played by each team under consideration.
5. The advisory committee should consider all games played.
6. The strength of each team's schedule should be given serious consideration.
7. Depth of material should be considered only if other factors are equal.


I few immediate thoughts:
I always wondered how the Thursday night game was decided and it turns out it had nothing to do with being the #1 overall seed, but was just like how MLB determined home field for the World Series.
I found it interesting that teams had to be pro-active and send a reply that they wanted to be considered.
The winners of the two WCHA sectionals were always selected for the NCAA tournament despite not being automatic selections.