I think Symmington would've swung MO over, and possibly enough cross-border support for IL too. Which would've made it 246 H - 247 N... and it would've gone to the house.
And the House in January, 1969 would have elected Humphrey President.
But with Illinois and Missouri going to Humphrey, this would have given Humphrey 229, Nixon 263.
Humphrey 191, plus Illinois 26, plus Missouri 12, total 229.
Nixon 301, minus Illinois 26, minus Missouri 12, total 263.
But the election would still go to the Democratically controlled House.