Comparing this election to the 1974 Post-Watergate election

From the National Journal:

Republicans picked up 680 seats in state legislatures, according to the National Conference of State Legislatures -- the most in the modern era. To put that number in perspective: In the 1994 GOP wave, Republicans picked up 472 seats. The previous record was in the post-Watergate election of 1974, when Democrats picked up 628 seats. . . .

For details on the NCSL numbers see this. Democrats also picked up 49 seats in the House that year, though that was presumably more difficult in that they already decisively controlled the House before the election with 242 seats. They also picked up a net gain of 3 seats in the Senate.