Six predecessor. They were a charter member of the Missouri Valley Intercollegiate Athletic Association (MVIAA) in 1907, from which the the Big Six broke away in 1928 (and later became the Big 7 and eventually the Big 8). But by then Iowa was long gone, having departed in 1911, after only 4 years in the MVIAA.
I think it would make more sense to put Iowa with the classic Big Ten schools, and move Penn State in with the northeastern schools, with their historical rival Pittsburgh. And I’d move Louisville into the spot Iowa vacated; makes sense for them to be paired up with Cincinnati, just up the road an hour or so away.