The Eagles played fantastic defense this season, finishing third in defensive S&P despite not having a single player on the unit who was rated higher than 3-stars by the recruiting services. You can read about their DL-based, multiple defense here.
Some lessons for Big 12 teams that'd like to be able to play defense that well who also don't have access to premier talent.
1. Getting sturdy DL that are violent with their hands goes a long, long ways towards building good defense. The Eagles DL are great at stunting in particular, which means they have a lot of pressures they can send that don't require sending numbers.
2. Culture matters. Addazio may have produced a crap offense this year but his physical style was undoubtedly instrumental in helping foster a culture that produced this defense. My next point will come back to this.
3. Convert corners into safeties. Adherence to "the rule of three" necessitates that teams recruit lots of physical, quality corners and convert some of them into safeties or else they risk being unable to hold up against B12 passing attacks. However, this teams need a physical culture that encourages the growth of corners into safeties that are willing to lay it all out in the alley.
4. The two-deep fire zone is a pretty nice tool in the arsenal if a team has the safeties to make it work. If they aren't rangy and good tacklers? Forget about it. But if they are it's a nice change-up for attacking QBs that are used to punishing blitzes based on single-high coverage.