re: How did the 12 SEC teams agree on these East & West permanent rivals for over a decade?

I can answer the MSU part

South Carolina was new and just randomly paired with MSU and they kept the newbies together.

Alabama had Tennessee, Auburn had Georgia and Florida, LSU wanted Florida

It was either Vanderbilt or Kentucky for MSU. Keep in mind, when these schedules were originally set, State was a top 25 club (They swept Texas in a home and home the first two years).

If you look at the '91 standings, the last of the 10-team SEC, State tied with Georgia for fourth and Kentucky went 0-7.

I won't argue that '98 State was one of the two worst SEC Championship participants ('95 Arkansas was terrible as well, but I think they had help via probation). But the West was awful that year. Four teams in the East would have won the West.

But unlike the '95 Hogs, State put up a fight in the actual championship game, and led midway through the fourth quarter.