Just for interest's sake, I thought I'd see exactly what each election would look like if a nationwide swing occurred in each of these elections to realize the popular vote found in each result. In cases where there are numerous undecideds, I'll scale up the D-R-I percentages such that they match the total percentage realized in the actual result (for example, if the actual result was 50-45 D-R, that makes the D-R votes 95% of the result, so a poll result of 35-40 D-R would get scaled up to 44.33-50.67 to match the 95% D-R portion of the total votes). This is, of course, not likely how the undecideds would actually break, but it's the best I can get without introducing bias through guessing how they would break.
So, to begin...
1964:
Lyndon B. Johnson (D) 50%
Barry Goldwater (R) 23%
The poll result of 50-23 equates to an election result of 68.16-31.36, which induces a 7.11% swing away from Goldwater to Johnson from the 1964 results.
Lyndon B. Johnson (D-TX) - 68.16% PV - 513 EVs (+27)
Barry Goldwater (R-AZ) - 31.36% PV - 25 EVs (-27)
1968:
Richard Nixon (R) 34%
Hubert H. Humphrey (D) 31%
George Wallace (I) 15%
The poll result of 34-31-15 equates to an election result of 42.36-38.62-18.69, which induces a 1.06% swing away from Nixon and a 4.10% swing away from Humphrey, both forming a 5.16% swing to Wallace, from the 1968 results.
Richard Nixon (R-CA*) - 42.36% PV - 327 EVs (+26)
Hubert H. Humphrey (D-MN) - 38.62% PV - 147 EVs (-44)
George Wallace (Am. Ind.-AL) - 18.69% PV - 64 EVs (+18)
*Or arguably R-NY. It makes little difference.
1972:
George McGovern (D) 42%
Richard Nixon (R) 39%
The poll result of 42-39 equates to an election result of 50.91-47.28, which induces a 13.39% swing away from Nixon to McGovern from the 1972 results.
George McGovern (D-SD) - 50.91% PV - 329 EVs (+311)
Richard Nixon (R-CA*) - 47.28% PV - 209 EVs (-311)
*Or arguably R-NY. It makes little difference.
1976:
Jimmy Carter (D) 52%
Gerald Ford (R) 35%
The poll result of 52-35 equates to an election result of 58.63-39.46, which induces a 8.55% swing away from Ford to Carter from the 1976 results.
Jimmy Carter (D-GA) - 58.63% PV - 519 EVs (+222)
Gerald Ford (R-MI) - 39.46% PV - 19 EVs (-222)
1980:
Ronald Reagan (R) 56%
Jimmy Carter (D) 30%
John Anderson (I) 6%
The poll result of 56-30-6 equates to an election result of 59.88-32.08-6.42, which induces a 8.93% swing away from Carter and a 0.19% swing away from Anderson, both forming a 9.13% to Reagan from the 1980 results.
Ronald Reagan (R-CA) - 59.88% PV - 535 EVs (+46)
Jimmy Carter (D-GA) - 32.08% PV - 3 EVs (-46)
John Anderson (I-IL) - 6.42% PV - 0 EVs (+/- 0)
1984:
Ronald Reagan (R) 64%
Walter Mondale (D) 24%
The poll result of 64-24 equates to an election result of 72.24-27.09, which induces a 13.47% swing away from Mondale to Reagan from the 1984 results.
Ronald Reagan (R-CA) - 72.24% PV - 535 EVs (+10)
Walter Mondale (D-MN) - 27.09% PV - 3 EVs (-10)
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This takes a long time and I really should be getting to bed; I'll do the remaining ones tomorrow if I have time.