So 1968 should be seen as a hard partisan realignment, with 1980 being more of a soft ideological realignment.
Why begin in 1968? 1952 is clearly a far more suitable starting point when discussing GOP inroads into the post-war South. It does after all mark the beginning of a proper two party system there with Eisenhower flipping a number of Southern states and drawing strength even from parts of the Deep South such as its "black belt" region (white voters there) and major urban areas. Even down-ballot races became more competitive prior to 68 as shown by the election of John Tower in 60 and the strong showing for Republicans in the 1962 Alabama and South Carolina senate races.
There has been an ongoing debate in US political history over how much of the Southern Realignment had to do with conservative Democrats switching parties over civil rights, and how much had to do with the growth of the New South, which was suburban, upper-middle-class, educated, and much more cosmopolitan than the Old South. These voters naturally gravitated towards the Republican party, just as their cohorts in the Northeast and (especially) the West. Suburban Atlanta, Dallas, and Charlotte start looking more and more like Orange County, CA, which I believe was already deeply Republican by 1952.
A great book that lays out this argument with a mountain of data is
The Silent Majority: Suburban Politics in the Sunbelt South by Matthew Lassiter
https://www.amazon.com/Silent-Majority-Suburban-Politics-Sunbelt/dp/0691133891