IOTL Gingrich managed it in 1994. With a POD between 1954 and 1980, make nationalization happen earlier. Bonus for before 1980, double bonus for before 1970.
Yes, but they were temporary. Otherwise Nixon, Reagan and GHWB would've brought in Republican Congresses on their coattails. That's what I want to see- a Democratic presidential landslide translates into Congress, and the same for Republican presidential landslides.
Again, they did. Bush Sr. didn't get big coattails because he was leading a third-term bid for his party, and coattail effects tend to decrease once a party has held the WH for sometime. Nixon and, especially, Reagan, did get big coattail effects - and remember, Reagan's flipped the Senate and gave him a working conservative majority in the House.
The major reason those didn't lead to actual takeovers of the House was because of the Southern Democrats. Otherwise House and Senate elections were fairly competitive. Having such a large chunk of seats safe for one party though made it difficult for Republicans to take control so long as Democrats were moderately competitive elsewhere.
That said, Congressional Democrats did benefit from some runs of good luck. The post-Watergate '74 election probably cemented Democratic control through '94. Had Watergate not occurred, the Democratic majority would have remained much more modest, and if you had a similar rotation in the presidency - Dem win in '76, Republican (Reagan) win in '80 - you could well have seen a GOP takeover that year.