During the wave of transparency and accountability reforms that were kicked off after Watergate, which included things like the Church Commission and the first federal campaign finance reform since TR, have someone push for IRV during the late Ford or early Carter Administration. Odds are the push would most likely come out of Congress and the pusher would need to be savvy, charismatic, and capable enough to build a strong coalition for it. Given the atmosphere, mistrust of government, and general cynicism which prevailed in the late 70s it's very possible IRV could be picked up and ran with as another means to rein in abuses of power by politicians.
The problem here is it's going to be tough to get Congress to go ahead with it. One of IRV's selling points is it gives minor parties a much better shot at the polls which is NOT in the best interests of the Democrats or the GOP. You'd need a lot of public outcry and pressure to force them to accept such a reform in that period or any other.