Testing my old age memory as I don't remember illini doing that well, and they didn't; as 1976 illini were 5-6 in 4 way tie for 3rd place. So if that is Top 10, that's really sad...
They're ranked very high because they played a hellacious schedule. Here are the end-of-season SRS rankings for each team they played matched up with the current team's rank of opponent quality:
#1 Michigan..........#4 Oregon
#3 Texas A&M..........#5 Penn State
#7 Ohio State..........#33 Kansas
#18 Missouri..........#34 Nebraska
#28 Baylor..........#35 Minnesota
#32 Minnesota..........#38 Michigan
#36 Wisconsin..........#53 Rutgers
#45 Purdue..........#83 Northwestern
#52 Michigan State..........#106 Purdue
#58 Iowa..........#119 Central Michigan
#92 Northwestern..........FCS Eastern Illinois
*Left off #75 Michigan State to compensate for the '76 team only playing 11 games.
So imagine the current team removing the EIU and CMU games and replacing them with #7 Notre Dame and #18 BYU, plus the bottom of your schedule being 15-20 spots better across the board.